Fluid Mechanics

Topic Information

Dear Colleagues,

Fluid mechanics has been a topic of great practical and research interest for many centuries.

Yet, this field of research is still young and vigorous, thanks to tremendous opprotunities that have been brought forward by modern computational and experimental techniques.

It is an amazingly wide and exciting area of knowledge, offering the possibility of applications in virtually every aspect of our lives. The present topical publication project offers the opportunity to communicate recent research results and application experiences across a wide range of sciences.

We are pleased to invite the research community to submit regular or review research papers on, but not limited to, the following relevant topics within the fluid mechanics space:

• Modern mathematical and computational methods of the investigation of fluid mechanics problems;
• Modern experimental techniques applicable to fluid mechanics;
• Instabilty and turbulence;
• Single- (fluid, gas) and multi-phase flows;
• Rheology;
• Lubrication;
• Magnetohydrodynamics;
• Plasma dynamics;
• Internal and external flows;
• Geophysical flows;
• Flows in industrial devices;
• Microfluid flows;
• Nanofluid flows;
• Filtration flows;
• Flows in biology and medicine;
• Flows of chemically reactive systems;
• Flows in aerospace applications;
• Compressible flows with shock waves, flows associated with explosions;
• Astrophysical flows.

Prof. Dr. Vasily Novozhilov
Prof. Dr. Cunlu Zhao
Topic Editors

Keywords

Participating Journals

Journal Name	Impact Factor	CiteScore	Launched Year	First Decision (median)	APC
Applied Sciences applsci	2.7	4.5	2011	16.9 Days	CHF 2400
Energies energies	3.2	5.5	2008	16.1 Days	CHF 2600
Fluids fluids	1.9	2.8	2016	20.7 Days	CHF 1800
Materials materials	3.4	5.2	2008	13.9 Days	CHF 2600
Mathematics mathematics	2.4	3.5	2013	16.9 Days	CHF 2600

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Published Papers (55 papers)

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28 pages, 450 KiB  

Open AccessReview

The Chimera Revisited: Wall- and Magnetically-Bounded Turbulent Flows

by Nils Tångefjord Basse

Fluids 2024, 9(2), 34; https://0-doi-org.brum.beds.ac.uk/10.3390/fluids9020034 - 30 Jan 2024

Viewed by 1346

Abstract

This review is a first attempt at bringing together various concepts from research on wall- and magnetically-bounded turbulent flows. Brief reviews of both fields are provided: The main similarities identified are coherent (turbulent) structures, flow generation, and transport barriers. Examples are provided and [...] Read more.

This review is a first attempt at bringing together various concepts from research on wall- and magnetically-bounded turbulent flows. Brief reviews of both fields are provided: The main similarities identified are coherent (turbulent) structures, flow generation, and transport barriers. Examples are provided and discussed. Full article

(This article belongs to the Topic Fluid Mechanics)

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14 pages, 4276 KiB  

Open AccessArticle

Modeling of the Flow Field and Clad Geometry of a Molten Pool during Laser Cladding of CoCrCuFeNi High-Entropy Alloys

by Dachuan Tian, Chonggui Li, Zhiguo Hu, Xintong Li, Yajun Guo, Xiaosong Feng, Zhenhai Xu, Xiaoguang Sun and Wenge Li

Materials 2024, 17(3), 564; https://0-doi-org.brum.beds.ac.uk/10.3390/ma17030564 - 25 Jan 2024

Viewed by 614

Abstract

A flow field analysis was performed in this research using the ANSYS Fluent module, and a dynamic heat source employing UDF was constructed using the DEFINE_PROFILE macro. A VOF model was developed to track the volume fraction of each fluid throughout the computational [...] Read more.

A flow field analysis was performed in this research using the ANSYS Fluent module, and a dynamic heat source employing UDF was constructed using the DEFINE_PROFILE macro. A VOF model was developed to track the volume fraction of each fluid throughout the computational domain as well as the steady-state or transient condition of the liquid–gas interface in the free liquid surface area. To determine the distribution state and regularity of the molten pool flow field, the flow field velocity was calculated iteratively by linking the Simple algorithm with the horizontal set method. The molten pool was concave, indicating that the key hole was distributed narrowly. Inserting cross-sections at different depths yielded the vector distribution of the molten pool flow velocity along the depth direction. We set up monitoring sites along the molten pool’s depth direction and watched the flow change over time. We investigated the effects of the process parameters on the flow field’s vector distribution. Full article

(This article belongs to the Topic Fluid Mechanics)

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27 pages, 17120 KiB  

Open AccessReview

From Navier to Stokes: Commemorating the Bicentenary of Navier’s Equation on the Lay of Fluid Motion

by Aldo Tamburrino

Fluids 2024, 9(1), 15; https://0-doi-org.brum.beds.ac.uk/10.3390/fluids9010015 - 06 Jan 2024

Cited by 1 | Viewed by 1343

Abstract

The article presents a summarised history of the equations governing fluid motion, known as the Navier–Stokes equations. It starts with the work of Castelli, who established the continuity equation in 1628. The determination of fluid flow resistance was a topic that involved the [...] Read more.

The article presents a summarised history of the equations governing fluid motion, known as the Navier–Stokes equations. It starts with the work of Castelli, who established the continuity equation in 1628. The determination of fluid flow resistance was a topic that involved the brightest minds of the 17th and 18th centuries. Navier’s contribution consisted of the incorporation of molecular attraction effects into Euler’s equation, giving rise to an additional term associated with resistance. However, his analysis was not the only one. This continued until 1850, when Stokes firmly established the boundary conditions that must be applied to the differential equations of motion, specifically stating the non-slip condition of the fluid in contact with a solid surface. With this article, the author wants to commemorate the bicentennial of the publication of “Sur les Lois du Mouvement des Fluides” by Navier in the Mémoires de l’Académie Royale des Sciences de l’Institut de France. Full article

(This article belongs to the Topic Fluid Mechanics)

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11 pages, 1476 KiB  

Open AccessBrief Report

Multiple Steady States in Laminar Rayleigh–Bénard Convection of Air

by Julien Carlier and Miltiadis V. Papalexandris

Fluids 2024, 9(1), 7; https://0-doi-org.brum.beds.ac.uk/10.3390/fluids9010007 - 26 Dec 2023

Viewed by 1246

Abstract

In this article, we report on numerical simulations of laminar Rayleigh–Bénard convection of air in cuboids. We provide numerical evidence of the existence of multiple steady states when the aspect ratio of the cuboid is sufficiently large. In our simulations, the Rayleigh number [...] Read more.

In this article, we report on numerical simulations of laminar Rayleigh–Bénard convection of air in cuboids. We provide numerical evidence of the existence of multiple steady states when the aspect ratio of the cuboid is sufficiently large. In our simulations, the Rayleigh number is fixed at $Ra=1.7\times {10}^4$. The gas in the cube is initially at rest but subject to random small-amplitude velocity perturbations and an adverse temperature gradient. When the flow domain is a cube, i.e., the aspect ratio is equal to unity, there is only one steady state. This state is characterized by the development of a single convective roll and by a symmetric normalized temperature profile with respect to the mid-height. On the contrary, when the aspect ratio is equal to 2, there are five different steady states. Only one of them exhibits a symmetric temperature profile and flow structure. The other four steady states are characterized by two-roll configurations and asymmetric temperature profiles. Full article

(This article belongs to the Topic Fluid Mechanics)

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26 pages, 5417 KiB  

Open AccessArticle

The Influence of Two-Dimensional Temperature Modulation on Floating Droplet Dynamics

by Alexander Nepomnyashchy and Ilya Simanovskii

Fluids 2024, 9(1), 6; https://0-doi-org.brum.beds.ac.uk/10.3390/fluids9010006 - 25 Dec 2023

Viewed by 1130

Abstract

We investigate the dynamics and instabilities of a droplet that floats on a liquid substrate. The substrate is cooled from below. In the framework of the slender droplet approximation and the precursor model, the problem is studied numerically. Oscillatory and stationary regimes of [...] Read more.

We investigate the dynamics and instabilities of a droplet that floats on a liquid substrate. The substrate is cooled from below. In the framework of the slender droplet approximation and the precursor model, the problem is studied numerically. Oscillatory and stationary regimes of thermocapillary convection have been observed. The influence of a two-dimensional spatial inhomogeneity of temperature on the droplet dynamics is investigated. The two-dimensional spatial temperature inhomogeneity can suppress oscillations, changing the droplet’s shape. In a definite region of parameters, the two-dimensional spatial modulation can lead to the excitation of periodic oscillations. The influence of the Biot number on the shape of the droplets is studied. Full article

(This article belongs to the Topic Fluid Mechanics)

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17 pages, 42401 KiB  

Open AccessArticle

Numerical Modeling of Two-Phase Flow inside a Wet Flue Gas Absorber Sump

by Nejc Vovk and Jure Ravnik

Energies 2023, 16(24), 8123; https://0-doi-org.brum.beds.ac.uk/10.3390/en16248123 - 18 Dec 2023

Viewed by 657

Abstract

A numerical model of a flue gas scrubber sump is developed with the aim of enabling optimization of the design of the sump in order to reduce energy consumption. In this model, the multiphase flow of the continuous phase, i.e., water, and the [...] Read more.

A numerical model of a flue gas scrubber sump is developed with the aim of enabling optimization of the design of the sump in order to reduce energy consumption. In this model, the multiphase flow of the continuous phase, i.e., water, and the dispersed phase, i.e., air bubbles, is considered. The air that is blown in front of the agitators, as well as the influence of the flow field of the agitators on the distribution of the dispersed phase and the recirculation pumps as outlet, is modeled. The bubble Sauter mean diameter is modeled using the population balance model. The model is used to analyze operating parameters such as the bubble retention time, the average air volume fraction, bubble Sauter mean diameter, the local distribution of the bubble size and the amount of air escaping from the pump outlets at two operating points. The purpose of the model is to simulate the two-phase flow in the sump of the flue gas scrubber using air dispersion technology with a combination of spargers and agitators, which, when optimized, reduces energy consumption by 33%. The results show that the homogeneity of air is lower in the bottom part of the absorber sump and that the amount of air escaping through recirculation pipes equals 1.2% of the total air blown into the absorber sump. The escaping air consists mainly of bubbles smaller than 6 mm. Additional operating point results show that halving the magnitude of the linear momentum source lowers the air retention, as well as the average homogeneity of the dispersed air. Full article

(This article belongs to the Topic Fluid Mechanics)

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16 pages, 9687 KiB  

Open AccessArticle

Experimental Investigation of the In-Cylinder Flow of a Compression Ignition Optical Engine for Different Tangential Port Opening Areas

by Mitsuhisa Ichiyanagi, Emir Yilmaz, Kohei Hamada, Taiga Hara, Willyanto Anggono and Takashi Suzuki

Energies 2023, 16(24), 8110; https://0-doi-org.brum.beds.ac.uk/10.3390/en16248110 - 17 Dec 2023

Cited by 1 | Viewed by 2021

Abstract

The push for decarbonization of internal combustion engines (ICEs) has spurred interest in alternative fuels, such as hydrogen and ammonia. To optimize combustion efficiency and reduce emissions, a closer look at the intake system and in-cylinder flows is crucial, especially when a hard-to-burn [...] Read more.

The push for decarbonization of internal combustion engines (ICEs) has spurred interest in alternative fuels, such as hydrogen and ammonia. To optimize combustion efficiency and reduce emissions, a closer look at the intake system and in-cylinder flows is crucial, especially when a hard-to-burn fuel, such as ammonia is utilized. In port fuel injection ICEs, airflow within cylinders profoundly affects combustion and emissions by influencing the air–fuel mixing phenomenon. Adjusting intake port openings is an important factor in controlling the in-cylinder airflow. In previous experiments with a transparent cylinder, tangential and helical ports demonstrated that varying the helical port’s opening significantly impacts flow velocities, swirl ratios, and swirl center positions (SCPs). In this study, we used a particle image velocimetry technique to investigate how the tangential port’s opening affects intake and in-cylinder flows. Flow velocities were assessed at different planes near the cylinder head, evaluating streamline maps, turbulent kinetic energy (TKE), and SCPs. Under the given experimental conditions, swirl flows were successfully generated early in the compression stroke when the tangential port opening exceeded 25%. Our findings emphasize the importance of minimizing TKE and SCP variation for successful swirl flow generation in engine cylinders equipped with both tangential and helical ports. Full article

(This article belongs to the Topic Fluid Mechanics)

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14 pages, 5191 KiB  

Open AccessArticle

The Experiments and Stability Analysis of Hypersonic Boundary Layer Transition on a Flat Plate

by Yanxin Yin, Yinglei Jiang, Shicheng Liu and Hao Dong

Appl. Sci. 2023, 13(24), 13302; https://0-doi-org.brum.beds.ac.uk/10.3390/app132413302 - 16 Dec 2023

Viewed by 749

Abstract

Experimental and linear stability theory (LST) investigation of boundary layer transition on a flat plate was conducted with a flow of Mach number 5. The temperature distributions and second-mode disturbances on the flat plate surface at different unit Reynolds number (Re_unit [...] Read more.

Experimental and linear stability theory (LST) investigation of boundary layer transition on a flat plate was conducted with a flow of Mach number 5. The temperature distributions and second-mode disturbances on the flat plate surface at different unit Reynolds number (Re_unit) values were captured by infrared thermography and PCB technology, respectively, which revealed the transition location of the flat-plate boundary layer. The PCB sensors successfully captured the second-mode disturbances within the boundary layer initially at a frequency of about 100 kHz, with a gradually expanding frequency range as the distance travelled downstream increased. The evolution characteristics of the second-mode instabilities were also investigated by LST and obtained for the second mode, ranging from 100 to 250 kHz. The amplitude amplification factor (N-factor) of the second-mode instabilities was calculated by the e^N method. The N-factor of the transition location in the wind tunnel experiment predicted by LST is about 0.98 and 1.25 for Re_unit = 6.38 × 10⁶ and 8.20 × 10⁶, respectively. Full article

(This article belongs to the Topic Fluid Mechanics)

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14 pages, 3084 KiB  

Open AccessArticle

Prediction of Flow Properties of Porous Triply Periodic Minimal Surface (TPMS) Structures

by Saúl Piedra, Arturo Gómez-Ortega and James Pérez-Barrera

Fluids 2023, 8(12), 312; https://0-doi-org.brum.beds.ac.uk/10.3390/fluids8120312 - 29 Nov 2023

Cited by 2 | Viewed by 1557

Abstract

The flow through geometrically complex structures is an important engineering problem. In this work, the laminar flow through Triply Periodic Minimal Surface (TPMS) structures is numerically analyzed using Computational Fluid Dynamics (CFD) simulations. Two different TPMS structures were designed, and their porosity was [...] Read more.

The flow through geometrically complex structures is an important engineering problem. In this work, the laminar flow through Triply Periodic Minimal Surface (TPMS) structures is numerically analyzed using Computational Fluid Dynamics (CFD) simulations. Two different TPMS structures were designed, and their porosity was characterized as a function of the isovalue. Then, CFD simulations were implemented to compute the pressure drop by systematically varying the flow velocity and the porosity of the structure. A Darcy–Forchheimer model was fitted to CFD results to calculate the inertial and permeability coefficients as functions of the porosity. These types of results can be very useful for designing fluid flow applications and devices (for instance, heat exchangers), as well as for integrating these TPMS structures since the flow can be very well estimated when using the porous medium model. Full article

(This article belongs to the Topic Fluid Mechanics)

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27 pages, 20425 KiB  

Open AccessArticle

Universal Form of Radial Hydraulic Machinery Four-Quadrant Equations for Calculation of Transient Processes

by Zdravko Giljen and Miloš Nedeljković

Energies 2023, 16(23), 7736; https://0-doi-org.brum.beds.ac.uk/10.3390/en16237736 - 23 Nov 2023

Viewed by 544

Abstract

Suter curves for the Wh and Wm characteristics and four-quadrant (4Q) diagrams of 11 radial pump–turbine models with different specific speeds (nq = 24.34, 24.8, 27, 28.6, 38, 41.6, 41.9, 43.83, 50, 56, and 64.04) are presented for the first time in [...] Read more.

Suter curves for the Wh and Wm characteristics and four-quadrant (4Q) diagrams of 11 radial pump–turbine models with different specific speeds (nq = 24.34, 24.8, 27, 28.6, 38, 41.6, 41.9, 43.83, 50, 56, and 64.04) are presented for the first time in this paper, as well as Suter curves for two pump models (nq = 25 and 41.8) previously published in the literature. All of these curves were analyzed to establish a certain universal law of behavior, depending on the specific speed. To determine such a law, a fitting procedure using regression and spline methods was carried out. This paper provides details of a research plan and structures (including data collection for four-quadrant diagrams for pump–turbine and pump models under different specific speeds nq), a procedure for re-calculating four-quadrant diagrams of the models as Suter curves for the Wh and Wm characteristics, definitions of the optimal points for pump and turbine operating modes in pump–turbine models under different specific speeds, and the development of numerical models in MATLAB to obtain a universal equation for the Wh and Wm characteristics. The scientific contribution of this paper is that it is the first to publish original mathematical curves using universal equations for the Wh and Wm characteristics of radial pumps and pump–turbines. The applicability of the equations is demonstrated by considering a pumping station in which two radial pumps were installed, for which the calculation of transient processes was performed using a numerical model developed in MATLAB by the authors. The transition process results are compared for two cases: first, when input data in the numerical model are used with the values of the Suter curves for the Wh and Wm characteristics obtained by re-calculating the four-quadrant operating characteristics (Q₁₁, n₁₁, M₁₁) at a given specific speed, and second, when the values of the Suter curves for the Wh and Wm characteristics are obtained from the universal equations. Full article

(This article belongs to the Topic Fluid Mechanics)

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17 pages, 10439 KiB  

Open AccessArticle

A Numerical Study on the Influence of Transverse Grooves on the Aerodynamic Performance of Micro Air Vehicles Airfoils

by Zhiping Li, Yueren Zuo, Haideng Zhang, Long He, Enbo Sun, Yuhan Long, Lifu Zhang and Peng Zhang

Appl. Sci. 2023, 13(22), 12371; https://0-doi-org.brum.beds.ac.uk/10.3390/app132212371 - 15 Nov 2023

Viewed by 665

Abstract

Micro Air Vehicles (MAVs) airfoils usually operate at low Reynolds number conditions, where viscous drag will consume a large amount of propulsion power. Due to the small dimensions, many drag reduction methods have failed, resulting in limited current research. To develop an effective [...] Read more.

Micro Air Vehicles (MAVs) airfoils usually operate at low Reynolds number conditions, where viscous drag will consume a large amount of propulsion power. Due to the small dimensions, many drag reduction methods have failed, resulting in limited current research. To develop an effective method of reducing viscous drag, transverse grooves were placed on the surface of MAVs airfoils in this study, and a numerical investigation was implemented to uncover the corresponding flow control law as well as the mechanism. Research has shown that transverse grooves have an impact on the drag and lift of airfoils. For drag, properly sized transverse grooves have the effect of reducing drag, but under high adverse pressure gradients or when the continuous arrangement of grooves is excessive, the optimal drag reduction effect achieved by the grooves is weakened, and even the drag increases due to the significant increase in pressure difference. In severe cases, it may also cause strong flow separation, which is not conducive to MAV flight. For lift, the boundary vortex in the groove has the ability to reduce the static pressure near the groove. However, high adverse pressure gradients or too many grooves will thicken the boundary layer and increase the blockage effect, resulting in a large static pressure on the grooved side of the airfoil (with an increase in drag). From the perspective of circulation, the static pressure changes on the suction and pressure surfaces have opposite effects on lift. Considering the comprehensive aerodynamic performance of the airfoil, we designed a high lift-to-drag ratio airfoil with grooves, which increased the lift-to-drag ratio by 33.747% compared to the smooth airfoil. Based on the conclusions, we proposed preliminary design criteria for grooved airfoils, providing guidance for subsequent research and applications. Full article

(This article belongs to the Topic Fluid Mechanics)

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21 pages, 7040 KiB  

Open AccessArticle

Internal Flow Prediction in Arbitrary Shaped Channel Using Stream-Wise Bidirectional LSTM

by Jaekyun Ko, Wanuk Choi and Sanghwan Lee

Appl. Sci. 2023, 13(20), 11481; https://0-doi-org.brum.beds.ac.uk/10.3390/app132011481 - 19 Oct 2023

Viewed by 712

Abstract

Deep learning (DL) methods have become the trend in predicting feasible solutions in a shorter time compared with traditional computational fluid dynamics (CFD) approaches. Recent studies have stacked numerous convolutional layers to extract high-level feature maps, which are then used for the analysis [...] Read more.

Deep learning (DL) methods have become the trend in predicting feasible solutions in a shorter time compared with traditional computational fluid dynamics (CFD) approaches. Recent studies have stacked numerous convolutional layers to extract high-level feature maps, which are then used for the analysis of various shapes under differing conditions. However, these applications only deal with predicting the flow around the objects located near the center of the domain, whereas most fluid-transport-related phenomena are associated with internal flows, such as pipe flows or air flows inside transportation vehicle engines. Hence, to broaden the scope of the DL approach in CFD, we introduced a stream-wise bidirectional (SB)-LSTM module that generates a better latent space from the internal fluid region by additionally extracting lateral connection features. To evaluate the effectiveness of the proposed method, we compared the results obtained using SB-LSTM to those of the encoder–decoder(ED) model and the U-Net model, as well as with the results when not using it. When SB-LSTM was applied, in the qualitative comparison, it effectively addressed the issue of erratic fluctuations in the predicted field values. Furthermore, in terms of quantitative evaluation, the mean relative error (MRE) for the x-component of velocity, y-component of velocity, and pressure was reduced by at least 2.7%, 4.7%, and 15%, respectively, compared to the absence of the SB-LSTM module. Furthermore, through a comparison of the calculation time, it was found that our approach did not undermine the superiority of the neural network’s computational acceleration effect. Full article

(This article belongs to the Topic Fluid Mechanics)

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17 pages, 29900 KiB  

Open AccessArticle

Mechanisms of Gravitational Influence on Weld Pool Behavior and Weld Bead Performance in Variable Polarity Plasma Arc Welding across Different Welding Position

by Jingbo Liu, Fan Jiang, Shujun Chen, Bin Xu, Guokai Zhang, Wei Cheng and Xinqiang Ma

Materials 2023, 16(19), 6457; https://0-doi-org.brum.beds.ac.uk/10.3390/ma16196457 - 28 Sep 2023

Viewed by 827

Abstract

This article comprehensively explores the cross-scale effects of gravity on macroscopic flow formation and weld bead formation in variable polarity plasma arc welding. Gravity-induced changes in welding direction were achieved through welding at different spatial positions. The properties of the weld bead were [...] Read more.

This article comprehensively explores the cross-scale effects of gravity on macroscopic flow formation and weld bead formation in variable polarity plasma arc welding. Gravity-induced changes in welding direction were achieved through welding at different spatial positions. The properties of the weld bead were investigated at various spatial locations. Additionally, an elemental tracing technique was employed to study the internal flow behavior of molten metal. In the flat welding position, there is an observable trend of increasing grain size in the welded bead, accompanied by a significant expansion of the coarse grain zone. Consequently, the properties of the weld bead in the flat position are inferior to those achieved in the vertical welding position. This phenomenon can be attributed to the accumulation of molten metal at the exit side of the keyhole, resulting in temperature accumulation. Research indicates that the internal flow within the weld pool plays a critical role in causing this phenomenon. The study’s findings reveal the presence of two distinct vortex flow patterns within the weld pool: one aligned with the welding direction and the other directed towards the interior of the weld pool. Particularly noteworthy is the substantial expansion of the flow channel area in the flat welding position, which significantly amplifies the impact of internal flow. This enhanced flow intensity inevitably leads to the increased buildup of molten metal at the keyhole exit side. These studies lay the groundwork for achieving high-quality and controllable spatial-position welding. Full article

(This article belongs to the Topic Fluid Mechanics)

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21 pages, 4891 KiB  

Open AccessReview

Under-Expanded Jets in Advanced Propulsion Systems—A Review of Latest Theoretical and Experimental Research Activities

by Francesco Duronio, Carlo Villante and Angelo De Vita

Energies 2023, 16(18), 6471; https://0-doi-org.brum.beds.ac.uk/10.3390/en16186471 - 07 Sep 2023

Cited by 1 | Viewed by 1272

Abstract

The current ongoing rise in environmental pollution is leading research efforts toward the adoption of propulsion systems powered by gaseous fuels like hydrogen, methane, e-fuels, etc. Although gaseous fuels have been used in several types of propulsion systems, there are still many aspects [...] Read more.

The current ongoing rise in environmental pollution is leading research efforts toward the adoption of propulsion systems powered by gaseous fuels like hydrogen, methane, e-fuels, etc. Although gaseous fuels have been used in several types of propulsion systems, there are still many aspects that can be improved and require further study. For this reason, we considered it important to provide a review of the latest research topics, with a particular focus on the injection process. In advanced engine systems, fuel supply is achieved via enhanced direct injection into the combustion chamber. The latter involves the presence of under-expanded jets. Under-expanded jets are a particular kind of compressible flow. For this reason, the review initially provides a brief physical explanation of them. Next, experimental and numerical CFD investigation techniques are discussed. The last section of this manuscript presents an analysis of the jet’s structure. The injection parameters commonly used are examined; next, the characteristics of the near-nozzle field are reviewed and finally, the far-field turbulent mixing, which strongly affects the air–fuel mixture formation process, is discussed. Full article

(This article belongs to the Topic Fluid Mechanics)

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9 pages, 547 KiB  

Open AccessCommunication

Hagen-Poiseuille Flow in a Quarter-Elliptic Tube

by Mateus D. Bacelar, Hugo C. M. G. Ferreira, Rajai S. Alassar and André B. Lopes

Fluids 2023, 8(9), 247; https://0-doi-org.brum.beds.ac.uk/10.3390/fluids8090247 - 07 Sep 2023

Viewed by 1242

Abstract

We present a rare exact solution of the Navier–Stokes equations for the Hagen–Poiseuille flow through a quarter-elliptic tube. Utilizing the separation of variables method, we derive the solution and report expressions for both the volumetric flow rate and the friction factor–Reynolds number product. [...] Read more.

We present a rare exact solution of the Navier–Stokes equations for the Hagen–Poiseuille flow through a quarter-elliptic tube. Utilizing the separation of variables method, we derive the solution and report expressions for both the volumetric flow rate and the friction factor–Reynolds number product. Full article

(This article belongs to the Topic Fluid Mechanics)

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13 pages, 2941 KiB  

Open AccessArticle

Investigation the Effect of MR Fluid Composition on Properties at Low Strain Ranges

by Anna Fenyk, Wojciech Horak and Marek Zieliński

Materials 2023, 16(17), 5730; https://0-doi-org.brum.beds.ac.uk/10.3390/ma16175730 - 22 Aug 2023

Viewed by 708

Abstract

The paper presents the results of eight magnetorheological (MR) fluids of different compositions. Magnetite and carbonyl iron were used as magnetic particles. MR fluids based on glycerin and OKS 352 oil were produced using stabilizers in the form of oleic acid and Aerosil [...] Read more.

The paper presents the results of eight magnetorheological (MR) fluids of different compositions. Magnetite and carbonyl iron were used as magnetic particles. MR fluids based on glycerin and OKS 352 oil were produced using stabilizers in the form of oleic acid and Aerosil 200 (Evonik Resource Efficiency GmbH, Hanau, Germany) silica; additives such as graphite and yellow dextrin were also used. The aim of the study was to determine the properties of various combinations of components on the dynamic properties of MR fluids, i.e., properties characterizing the fluid within the range of low deformations, as well as to investigate the effect of different compositions on structural yield stress and flow stress prepared MR fluids at different magnetic field induction values. Full article

(This article belongs to the Topic Fluid Mechanics)

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20 pages, 8556 KiB  

Open AccessArticle

Numerical Investigation of the Cavitation Characteristics in Venturi Tubes: The Role of Converging and Diverging Sections

by Yi Liu and Bin Li

Appl. Sci. 2023, 13(13), 7476; https://0-doi-org.brum.beds.ac.uk/10.3390/app13137476 - 25 Jun 2023

Cited by 1 | Viewed by 1165

Abstract

Cavitation is a typical physical process that has shown to be highly valuable in the wastewater treatment field. This study aims to investigate the effects of the converging and diverging sections of a Venturi tube on the cavitation flow field. Multiphase flows in [...] Read more.

Cavitation is a typical physical process that has shown to be highly valuable in the wastewater treatment field. This study aims to investigate the effects of the converging and diverging sections of a Venturi tube on the cavitation flow field. Multiphase flows in tubes are presented using the mixture model and the standard k-ε model. And the Schnerr and Sauer cavitation model is employed to simulate the vapor–liquid phase transition process. Both grid independence and the numerical method’s feasibility were validated before the research. The results showed that the influence of the divergence section length on Venturi cavitation characteristics depends on the provided pressure conditions. As the pressure increases, shorter divergence sections result in more significant cavitation effects. The length of the convergence section displays various cavitation behaviors under different pressure situations. A small contraction section length can achieve better cavitation effects in high-pressure applications, whereas the opposite is true in low-pressure cases. Within the scope of this study, it was observed that the Venturi tube with a divergent section of 14 Lt and a convergent one of 2.4 Lt provided enhanced cavitation performance when subjected to inlet pressures ranging from 0.8 to 1.2 MPa. Our findings indicate that the selection of converging and diverging section lengths in Venturi tubes should consider the corresponding operational pressure conditions, which provides valuable guidance and engineering significance in the research and development of Venturi cavitation devices in hydraulic engineering. Full article

(This article belongs to the Topic Fluid Mechanics)

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16 pages, 10378 KiB  

Open AccessArticle

Aerodynamic Characteristics Analysis of Rectifier Drum of High-Speed Train Environmental Monitoring Devices

by Baowang Li, Xiaobing Wang, Junqiang Wu, Yang Tao and Neng Xiong

Appl. Sci. 2023, 13(12), 7325; https://0-doi-org.brum.beds.ac.uk/10.3390/app13127325 - 20 Jun 2023

Viewed by 797

Abstract

To study the aerodynamic characteristics of the convex structure of a surface-monitoring device on a high-speed train and to evaluate its impact on the aerodynamic performance of the high-speed train, numerical simulation research was conducted on three different layouts of the monitoring device. [...] Read more.

To study the aerodynamic characteristics of the convex structure of a surface-monitoring device on a high-speed train and to evaluate its impact on the aerodynamic performance of the high-speed train, numerical simulation research was conducted on three different layouts of the monitoring device. The computational fluid dynamics (CFD) method was used for the simulation study, and the unsteady compressible NS equation was used as the control equation. Hexagonal grid technology was used to reduce the demand for the grid quantity. The rationality of the grid size and layout was verified through grid independence research. To increase the accuracy of the numerical simulation, the γ-Re_θ transition model and improved delayed detached eddy simulation (IDDES) method were coupled for the simulation research. The aerodynamic characteristics of the different operation directions and configurations were compared and analyzed. The research results showed that the windward side of the single pantograph detection device experienced positive pressure, and the sideline and leeward sides experienced negative pressure. Increasing the fillet radius of the sideline could appropriately reduce the aerodynamic resistance. When the speed was about 110 m/s, the drag force coefficient of the detection device was 210~410 N, and the lateral force was small, which means that it had little impact on the overall aerodynamic force of the train. According to the results of the unsteady analysis of the layout with a large space, the resistance during forward travel was greater than that during negative travel. The streamlined upwind surface was conducive to reducing the scope of the leeward separation zone and the amplitude of the pressure fluctuation in the leeward zone, and it thus reduced the resistance. For the running trains, a vortex was formed on their leeward surface. The pressure monitoring results showed that the separated airflow had no dominant frequency or energy peak. The possibility of the following train top and other components experiencing resonance damage is low. Full article

(This article belongs to the Topic Fluid Mechanics)

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20 pages, 13230 KiB  

Open AccessArticle

Experimental Detection of Organised Motion in Complex Flows with Modified Spectral Proper Orthogonal Decomposition

by Nick Schneider, Simon Köhler and Jens von Wolfersdorf

Fluids 2023, 8(6), 184; https://0-doi-org.brum.beds.ac.uk/10.3390/fluids8060184 - 17 Jun 2023

Cited by 1 | Viewed by 955

Abstract

Spectral proper orthogonal decomposition (SPOD) has seen renewed interest in recent years due to its unique ability to decouple organised motion at different timescales from large datasets with limited available information. This paper investigated the unsteady components of the flow field within a [...] Read more.

Spectral proper orthogonal decomposition (SPOD) has seen renewed interest in recent years due to its unique ability to decouple organised motion at different timescales from large datasets with limited available information. This paper investigated the unsteady components of the flow field within a simplified turbine centre frame (TCF) model by applying SPOD to experimental, time-resolved flow speed data captured by particle image velocimetry (PIV). It was observed that conventional methods failed to capture the two significant active bands in the power spectrum predicted by preliminary hot wire anemometry measurements. Therefore, a modification to the SPOD procedure, which employs subsampling of the time sequence recorded in the experiment to artificially lower the PIV data acquisition frequency, was developed and successfully deployed to analyse the TCF flow field. The two dynamically active bands were identified in the power spectra, resulting in a closer match to the preceding analyses. Within these bands, SPOD’s ability to capture spatial coherence was leveraged to detect several plausible coherent, fluctuating structures in two perpendicular planes. A partial three-dimensional reconstruction of the flow phenomena suggested that both bands were associated with a distinct mode of organised motion, each contributing a significant percentage of the system’s total fluctuating energy. Full article

(This article belongs to the Topic Fluid Mechanics)

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28 pages, 25522 KiB  

Open AccessArticle

Compressible and Viscous Effects in Transonic Planar Flow around a Circular Cylinder—A Numerical Analysis Based on a Commercially Available CFD Tool

by Jana Hoffmann and Daniel A. Weiss

Fluids 2023, 8(6), 182; https://0-doi-org.brum.beds.ac.uk/10.3390/fluids8060182 - 14 Jun 2023

Cited by 1 | Viewed by 1528

Abstract

Transonic planar flows around a circular cylinder are investigated numerically for laminar and turbulent flow conditions with Reynolds numbers of $50\le R{e}_D\le 300$ and $8890\le R{e}_D\le$ 80,000 and free stream Mach numbers in the range [...] Read more.

Transonic planar flows around a circular cylinder are investigated numerically for laminar and turbulent flow conditions with Reynolds numbers of $50\le R{e}_D\le 300$ and $8890\le R{e}_D\le$ 80,000 and free stream Mach numbers in the range of $0.2\le M{a}_{\infty }\le 2$. A commercially available CFD tool is used and validated for this purpose. The results show that the flow phenomena occurring can be grouped into eight regimes. Compared to the incompressible flow regimes, several new phenomena can be found. In contrast, at higher $M{a}_{\infty }$ of $0.6\le M{a}_{\infty }\le 0.8$ vortices in the wake of the cylinder are suppressed for $R{e}_D=50$. In some cases, $M{a}_{\infty }=0.8$ and $R{e}_D\ge 300$, $\lambda$-shocks are formed in the near cylinder wake. For supersonic $M{a}_{\infty }$, two different phenomena are observed. Beside the well-known oblique and detached shocks, for $50\le R{e}_D\le 300$ a wake with instabilities is formed downstream of the cylinder. Furthermore, the temporal mean drag coefficient ${\overline{C}}_{\mathrm{D}}$, the Strouhal number $Str$, as well as the critical Mach number $M{a}_{\mathrm{crit}}$ are calculated from the simulation results and are interpreted. Full article

(This article belongs to the Topic Fluid Mechanics)

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30 pages, 3667 KiB  

Open AccessArticle

Bifurcation Analysis and Propagation Conditions of Free-Surface Waves in Incompressible Viscous Fluids of Finite Depth

by Arash Ghahraman and Gyula Bene

Fluids 2023, 8(6), 173; https://0-doi-org.brum.beds.ac.uk/10.3390/fluids8060173 - 31 May 2023

Cited by 1 | Viewed by 1108

Abstract

Viscous linear surface waves are studied at arbitrary wavelength, layer thickness, viscosity, and surface tension. We find that in shallow enough fluids no surface waves can propagate. This layer thickness is determined for some fluids, water, glycerin, and mercury. Even in any thicker [...] Read more.

Viscous linear surface waves are studied at arbitrary wavelength, layer thickness, viscosity, and surface tension. We find that in shallow enough fluids no surface waves can propagate. This layer thickness is determined for some fluids, water, glycerin, and mercury. Even in any thicker fluid layers, propagation of very short and very long waves is forbidden. When wave propagation is possible, only a single propagating mode exists for a given horizontal wave number. In contrast, there are two types of non-propagating modes. One kind of them exists at all wavelength and material parameters, and there are infinitely many such modes for a given wave number, distinguished by their decay rates. The other kind of non-propagating mode that is less attenuated may appear in zero, one, or two specimens. We notice the presence of two length scales as material parameters, one related to viscosity and the other to surface tension. We consider possible modes for a given material on the parameter plane layer thickness versus wave number and discuss bifurcations among different mode types. Motion of surface particles and time evolution of surface elevation is also studied at various parameters in glycerin, and a great variety of behaviour is found, including counterclockwise surface particle motion and negative group velocity in wave propagation. Full article

(This article belongs to the Topic Fluid Mechanics)

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22 pages, 44360 KiB  

Open AccessArticle

Effects of “S”-Type Bowed Guide Vanes on Unsteady Flow in 1.5-Stage Axial Compressors

by Yupeng Liu, Guangqing Liao, Yunzhu Li, Yonghui Xie and Di Zhang

Appl. Sci. 2023, 13(8), 5071; https://0-doi-org.brum.beds.ac.uk/10.3390/app13085071 - 18 Apr 2023

Viewed by 915

Abstract

In axial compressors, the unsteady flow caused by the interaction between dynamic and static cascades will make the moving vanes subject to periodic forces and increase the risk of high-cycle fatigue fractures. In this study, an “S”-type bowed guide vane was designed and [...] Read more.

In axial compressors, the unsteady flow caused by the interaction between dynamic and static cascades will make the moving vanes subject to periodic forces and increase the risk of high-cycle fatigue fractures. In this study, an “S”-type bowed guide vane was designed and a 1.5-stage axial compressor model was established. For five guide vanes with different bending coefficients, unsteady numerical simulation was carried out under design conditions and near-blockage conditions. The influence of the guide vane bending coefficient on the pressure ratio and efficiency is analyzed, and the aerodynamic exciting force on moving vanes is analyzed by using the fast Fourier transform. The study shows that the model with an “S”-type bowed guide vane can greatly reduce the amplitude of aerodynamic exciting force on moving vanes. The model with a guide vane bending coefficient of −10 mm can reduce the tangential and axial aerodynamic exciting force amplitudes at the first-order blade-passing frequency by 90.82% and 90.39% under the design conditions, respectively. Under the near-blockage condition, the tangential and axial aerodynamic exciting force amplitudes can be reduced by 85.84% and 86.58%, respectively. This can greatly improve the vibration safety of the moving vane. Full article

(This article belongs to the Topic Fluid Mechanics)

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14 pages, 5344 KiB  

Open AccessTechnical Note

Hydraulic Performance of Wave-Type Flow at a Sill-Controlled Stilling Basin

by Yu Zhou, Jianhua Wu, Hai Zhao, Jianyong Hu and Fuqing Bai

Appl. Sci. 2023, 13(8), 5053; https://0-doi-org.brum.beds.ac.uk/10.3390/app13085053 - 18 Apr 2023

Cited by 1 | Viewed by 986

Abstract

Downstream of the sluice gate or weir, wave-type flows inevitably occur in stilling basins with no tailwater. This paper aims to investigate the hydraulic performance of wave-type flows at a sill-controlled stilling basin through experimental research. The flow pattern, bottom pressure profiles along [...] Read more.

Downstream of the sluice gate or weir, wave-type flows inevitably occur in stilling basins with no tailwater. This paper aims to investigate the hydraulic performance of wave-type flows at a sill-controlled stilling basin through experimental research. The flow pattern, bottom pressure profiles along the stilling basin, and the air concentrations on the bottom and the sidewall were examined in five sill-controlled stilling basins by altering the sill position and the height. The results show that wave-type flow patterns contain submerged and non-submerged jumps, which are relevant to ambient pressure head and air entrainment. The bottom pressure profiles are related to larger pressure fluctuations at large unit discharges and two peak pressure values in the vicinity of the sill. The air concentrations on the bottom and the sidewall decrease with the increasing unit discharge. The flow zone in the vicinity of the sill should be focused upon concerning protection against cavitation damage because of the slight air entrainment and significant pressure fluctuations. These findings advance our understanding of wave-type flows, and their ambient pressure heads and air entrainment are useful for designing the sill-controlled stilling basin in hydraulic engineering. Full article

(This article belongs to the Topic Fluid Mechanics)

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13 pages, 4081 KiB  

Open AccessArticle

Detailed Analysis of Airflow Generated by High Voltage on a Point-Tube Electrode Geometry

by Jiří Primas, Michal Malík, Pavel Pokorný, Josef Novák, Petr Parma, Filip Sanetrník and Petr Schovanec

Fluids 2023, 8(4), 115; https://0-doi-org.brum.beds.ac.uk/10.3390/fluids8040115 - 31 Mar 2023

Viewed by 1432

Abstract

This paper is focused on the research of airflow generating through the use of high-voltage electrohydrodynamic devices. For this purpose, the authors built several electrohydrodynamic airflow generators with one point electrode and one tube electrode of varying dimensions and compared their efficiency in [...] Read more.

This paper is focused on the research of airflow generating through the use of high-voltage electrohydrodynamic devices. For this purpose, the authors built several electrohydrodynamic airflow generators with one point electrode and one tube electrode of varying dimensions and compared their efficiency in generating the airflow in order to find an optimal design. The character of the flow was also analyzed with the help of particle image velocimetry, and velocity vector maps and velocity profile were acquired. In addition, a possible practical cooling application was proposed and realized with positive results. Lastly, the products present in the generated airflow were tested for ozone and nitrogen oxides, which could have detrimental effects on human health and material integrity. In both cases, the concentration has been found to be below permissible limits. Full article

(This article belongs to the Topic Fluid Mechanics)

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14 pages, 3014 KiB  

Open AccessArticle

Study of the Influence of Dynamic and Static Capillary Forces on Production in Low-Permeability Reservoirs

by Yuanzhang Zhang, Youqi Wang, Jianwen Gao, Yuehua Cui and Shuoliang Wang

Energies 2023, 16(3), 1554; https://0-doi-org.brum.beds.ac.uk/10.3390/en16031554 - 03 Feb 2023

Viewed by 1264

Abstract

Low-permeability reservoirs have strong heterogeneity, and the production prediction based on traditional seepage model is not accurate enough. The dynamic capillary-force seepage model can characterize the dynamic heterogeneity of seepage and more accurately describe the oil–water flow process. In this paper, the calculation [...] Read more.

Low-permeability reservoirs have strong heterogeneity, and the production prediction based on traditional seepage model is not accurate enough. The dynamic capillary-force seepage model can characterize the dynamic heterogeneity of seepage and more accurately describe the oil–water flow process. In this paper, the calculation formula of the dynamic capillary force is obtained through a real low-permeability core experiment, and the seepage model of dynamic capillary force is established. Based on the model, the authors quantitatively study the effects of formation pressure, heterogeneity and production speed on dynamic capillary force through numerical solutions. It is found that compared with the traditional static capillary-force seepage model, the dynamic capillary-force seepage model makes the predicted water cut increase and the recovery factor decrease. With the increase in development time, formation pressure and production rate will make the effect of dynamic capillary force more obvious. According to the comparison of heterogeneous reservoir models, results show that the horizontal heterogeneity will strengthen the dynamic capillary-force effect, while the vertical heterogeneity will weaken the dynamic capillary-force effect. In the range of research parameters, the recovery ratio predicted by the dynamic capillary-force seepage model can be reduced by 4.7%. A new oil–water seepage model is proposed, which can characterize the spatial difference and dynamic change of low-permeability reservoirs with time. It is of great significance for describing the remaining oil distribution of low-permeability reservoirs in detail and making decisions on efficient EOR measures. Full article

(This article belongs to the Topic Fluid Mechanics)

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17 pages, 17886 KiB  

Open AccessArticle

A Numerical Study on the Characteristics of the Pressurized Water Reactor’s (PWR) Primary Moisture Separator Using the Particle Tracking Method

by Hongwu Zhao, Jun-Ho Jeon, Dong-In Yu and Yeon-Won Lee

Energies 2023, 16(3), 1310; https://0-doi-org.brum.beds.ac.uk/10.3390/en16031310 - 26 Jan 2023

Cited by 1 | Viewed by 1102

Abstract

The primary moisture separator—a key component in the PWR nuclear power plant—determines the quality of supplied steam to a turbine. Investigating its characteristics is important because supplying steam with excessive droplet entrainment results in damages to pipes, valves, and turbines in power plant [...] Read more.

The primary moisture separator—a key component in the PWR nuclear power plant—determines the quality of supplied steam to a turbine. Investigating its characteristics is important because supplying steam with excessive droplet entrainment results in damages to pipes, valves, and turbines in power plant circuits. In this numerical study, the particle tracking method in the Eulerian–Lagrangian methodology is used to investigate the characteristics of a primary moisture separator. Various swirl vanes with different bending angles, vane quantities, and vane locations are chosen to investigate the effect of design parameters on characteristics of the primary moisture separator. Additionally, the water droplet size is considered to vary from 0.01 to 50 $\mathsf{\mu }$m in this study. The pressure drop between the inlet and outlet, the steam quality at the orifice outlet, and the particle collection ratio are discussed in this paper. The results show that steam quality increases as the bending angle decreases, and increasing the number of swirl vanes increases both the pressure drop and the steam quality. Full article

(This article belongs to the Topic Fluid Mechanics)

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17 pages, 8736 KiB  

Open AccessArticle

Numerical Simulation of Carbon Dioxide–Nitrogen Mixture Dissolution in Water-Saturated Porous Media: Considering Cross-Diffusion Effects

by Saeed Mahmoodpour, Mrityunjay Singh, Ramin Mahyapour, Sina Omrani and Ingo Sass

Fluids 2023, 8(1), 22; https://0-doi-org.brum.beds.ac.uk/10.3390/fluids8010022 - 06 Jan 2023

Cited by 3 | Viewed by 1530

Abstract

The possibility of impure carbon dioxide (CO₂) sequestration can reduce the cost of these projects and facilitate their widespread adoption. Despite this, there are a limited number of studies that address impure CO₂ sequestration aspects. In this study, we examine [...] Read more.

The possibility of impure carbon dioxide (CO₂) sequestration can reduce the cost of these projects and facilitate their widespread adoption. Despite this, there are a limited number of studies that address impure CO₂ sequestration aspects. In this study, we examine the convection–diffusion process of the CO₂–nitrogen (N₂) mixture dissolution in water-saturated porous media through numerical simulations. Cross-diffusion values, as the missing parameters in previous studies, are considered here to see the impact of N₂ impurity on dissolution trapping in more realistic conditions. Homogeneous porous media are used to examine this impact without side effects from the heterogeneity, and then simulations are extended to heterogeneous porous media, which are a good representative of the real fields. Heterogeneity in the permeability field is generated with sequential Gaussian simulation. Using the averaged dissolved CO₂ and dissolution fluxes for each case, we could determine the onset of different dissolution regimes and behaviors of dissolution fluxes in CO₂–N₂ mixture dissolution processes. The results show that there is a notable difference between the pure cases and impure cases. Additionally, a failure to recognize the changes in the diffusion matrix and cross-diffusion effects can result in significant errors in the dissolution process. At lower temperatures, the N₂ impurity decreases the amount and flux of CO₂ dissolution; however, at higher temperatures, sequestrating the CO₂–N₂ mixture would be a more reasonable choice due to enhancing the dissolution behavior and lowering the project costs. The results of the heterogeneous cases indicate that heterogeneity, in most cases, reduces the averaged dissolved CO₂, and dissolution flux and impedes the onset of convection. We believe that the results of this study set a basis for future studies regarding the CO₂–N₂ mixture sequestration in saline aquifers. Full article

(This article belongs to the Topic Fluid Mechanics)

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19 pages, 7724 KiB  

Open AccessArticle

Self-Starting Characteristics and Flow-Induced Rotation of Single- and Dual-Stage Vertical-Axis Wind Turbines

by Muhammad Saif Ullah Khalid, David Wood and Arman Hemmati

Energies 2022, 15(24), 9365; https://0-doi-org.brum.beds.ac.uk/10.3390/en15249365 - 10 Dec 2022

Cited by 2 | Viewed by 1795

Abstract

Despite offering promising opportunities for wind energy harvesting in urban environments, vertical axis wind turbines face limitations in terms of poor starting characteristics. In this study, we focus on analyzing improvements offered by dual-stage turbines for a range of wind velocities. Numerical simulations [...] Read more.

Despite offering promising opportunities for wind energy harvesting in urban environments, vertical axis wind turbines face limitations in terms of poor starting characteristics. In this study, we focus on analyzing improvements offered by dual-stage turbines for a range of wind velocities. Numerical simulations are performed for different phase angles between the rotors (a measure of relative angular positions of the blades in the two rotors) to quantify the response time for their starting behavior. These simulations rely on a through sliding mesh technique coupled with flow-induced rotations. We find that for $U_{\infty }=4$$\mathrm{m}/\mathrm{s}$, the phase angles of ${30}^{\circ }$ and ${90}^{\circ }$ substantially reduce starting time in comparison to a single-stage turbine. Dual-stage turbines with a phase angle of ${90}^{\circ }$ exhibit similar or better starting behavior for other wind speeds. The phase angle of $0^{\circ }$ in double-rotor turbines shows the poorest starting response. Moreover, it is revealed that stabilization of shear layers generated by the blades passing through the windward side of the turbine, vortex-entrapment by these rotating blades, and suppressing of flow structures in the middle of the wake enhance the capacity of VAWTs to achieve faster steady angular speed. Full article

(This article belongs to the Topic Fluid Mechanics)

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14 pages, 3164 KiB  

Open AccessArticle

Thermodynamic and Spectroscopic Studies of SDS in Cinnamaldehyde + Ethanol Mixtures: Influences of Temperature and Composition

by Waleed M. Alamier, Shadma Tasneem, Arshid Nabi, Nazim Hasan and Firdosa Nabi

Appl. Sci. 2022, 12(23), 12020; https://0-doi-org.brum.beds.ac.uk/10.3390/app122312020 - 24 Nov 2022

Cited by 2 | Viewed by 1356

Abstract

The study of intermolecular interactions between ethanol (E-OH), cinnamaldehyde (CAD) with anionic surfactant sodium dodecyl sulfate (SDS) in non-aqueous media has been examined by utilizing conductometric and spectroscopic techniques. The critical micelle concentration (CMC) values have been determined. The experimental conductance data were [...] Read more.

The study of intermolecular interactions between ethanol (E-OH), cinnamaldehyde (CAD) with anionic surfactant sodium dodecyl sulfate (SDS) in non-aqueous media has been examined by utilizing conductometric and spectroscopic techniques. The critical micelle concentration (CMC) values have been determined. The experimental conductance data were analyzed against temperature and concentration using standard relations. The pseudo phase separation model has been adopted to calculate various thermodynamic parameters like standard free energy, ∆G°_mic, enthalpy, ∆H°_mic, and entropy, ∆S°_mic, of micelle formation. Fourier transforms infrared analysis (FTIR), and Fluorescence spectra were taken out to assess the possible interactions prevailing in the micellar systems. The findings demonstrated that the presence of SDS, and the composition of CAD + ethanol might affect the thermodynamic parameters. The discrepancy in these parameters with the surfactant concentration or with the temperature change indicates the manifestation of different interactions prevailing in the studied systems. Full article

(This article belongs to the Topic Fluid Mechanics)

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21 pages, 7134 KiB  

Open AccessArticle

Numerical Study on the Flow Past Three Cylinders in Equilateral-Triangular Arrangement at Re = 3 × 10⁶

by Mohan Zhang, Bo Yin, Dilong Guo, Zhanling Ji and Guowei Yang

Appl. Sci. 2022, 12(22), 11835; https://0-doi-org.brum.beds.ac.uk/10.3390/app122211835 - 21 Nov 2022

Cited by 4 | Viewed by 1522

Abstract

One of the most common systems in engineering problems is the multi-column system in the form of an equilateral-triangular arrangement. This study used three-dimensional numerical simulations to investigate the flow around three cylinders in this arrangement at the super-critical Reynolds number [...] Read more.

One of the most common systems in engineering problems is the multi-column system in the form of an equilateral-triangular arrangement. This study used three-dimensional numerical simulations to investigate the flow around three cylinders in this arrangement at the super-critical Reynolds number $Re=3\times {10}^6$, concentrating on the influence on the spacing ratio ($L/D$) among cylinders. The instantaneous vortex structures, Strouhal numbers, fluid force coefficients, and pressure distributions are analyzed thoroughly. The present study demonstrated that fluid dynamics is sensitive to $L/D$, by which five different flow patterns are classified, namely single bluff body flow ($L/D\le 1.1$), deflected gap flow ($1.2\le L/D\le 1.4$), anti-phase flow ($1.5\le L/D\le 2.3$), in-phase flow ($2.5\le L/D<3.5$), and co-shedding flow ($L/D\ge 3.5$). Critical bounds are identified by significant transitions in the flow structure, discontinuous drop and jump of $St$, and force coefficients. Full article

(This article belongs to the Topic Fluid Mechanics)

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18 pages, 1088 KiB  

Open AccessArticle

Unsteady Water-Based Ternary Hybrid Nanofluids on Wedges by Bioconvection and Wall Stretching Velocity: Thermal Analysis and Scrutinization of Small and Larger Magnitudes of the Thermal Conductivity of Nanoparticles

by Isaac Lare Animasaun, Qasem M. Al-Mdallal, Umair Khan and Ali Saleh Alshomrani

Mathematics 2022, 10(22), 4309; https://0-doi-org.brum.beds.ac.uk/10.3390/math10224309 - 17 Nov 2022

Cited by 27 | Viewed by 1707

Abstract

The uniqueness of nanofluids in the field of thermal analysis and engineering is associated with their thermal conductivity and thermodynamics. The dynamics of water made up of (i) single-walled carbon nanotubes with larger magnitudes of thermal conductivity of different shapes (i.e., platelet, cylindrical, [...] Read more.

The uniqueness of nanofluids in the field of thermal analysis and engineering is associated with their thermal conductivity and thermodynamics. The dynamics of water made up of (i) single-walled carbon nanotubes with larger magnitudes of thermal conductivity of different shapes (i.e., platelet, cylindrical, and spherical) and (ii) moderately small magnitudes of thermal conductivity (i.e., platelet magnesium oxide, cylindrical aluminum oxide, spherical silicon dioxide) were explored in order to address some scientific questions. In continuation of the exploration and usefulness of ternary hybrid nanofluid in hydrodynamics and geothermal systems, nothing is known on the comparative analysis between the two dynamics outlined above due to the bioconvection of static wedges and wedges with stretching at the wall. Reliable and valid numerical solutions of the governing equation that models the transport phenomena mentioned above are presented in this report. The heat transfer through the wall increased with the wall stretching velocity at a smaller rate of $0.52$ and a higher rate of $0.59$ when the larger and smaller thermal conductivity of nanoparticles were used, respectively. Larger or smaller magnitudes of the thermal conductivity of nanoparticles were used; the wall stretching velocity had no significant effects on the mass transfer rate but the distribution of the gyrotactic microorganism was strongly affected. Increasing the stretching at the wedge’s wall in the same direction as the transport phenomenon is suitable for decreasing the distribution of temperature owing to the higher velocity of ternary hybrid nanofluids either parallel or perpendicular to the wedge. Full article

(This article belongs to the Topic Fluid Mechanics)

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21 pages, 12753 KiB  

Open AccessArticle

Flood Prediction with Two-Dimensional Shallow Water Equations: A Case Study of Tongo-Bassa Watershed in Cameroon

by Alain Joel Elong, Ling Zhou, Bryan Karney, Haoyu Fang, Yun Cao and Steve L. Zeh Assam

Appl. Sci. 2022, 12(22), 11622; https://0-doi-org.brum.beds.ac.uk/10.3390/app122211622 - 16 Nov 2022

Cited by 4 | Viewed by 1419

Abstract

As a result of urbanization, combined with the anthropogenic effects of climate change, natural events such as floods are showing increasingly adverse impacts on human existence. This study proposes a new model, based on shallow water equations, that is able to predict these [...] Read more.

As a result of urbanization, combined with the anthropogenic effects of climate change, natural events such as floods are showing increasingly adverse impacts on human existence. This study proposes a new model, based on shallow water equations, that is able to predict these floods and minimize their impacts. The first-order finite volume method (FVM), the Harten Lax and van Leer (HLL) scheme, and the monotone upwind scheme for conservation laws (MUSCL) are applied in the model. In addition, a virtual boundary cell approach is adopted to achieve a monotonic solution for both interior and boundary cells and flux computations at the boundary cells. The model integrates the infiltration parameters recorded in the area, as well as the Manning coefficient specific to each land-cover type of the catchment region. The results provided were mapped to highlight the potential flood zones and the distribution of water heights throughout the catchment region at any given time, as well as that at the outlet. It has been observed that when standard infiltration and the Manning parameters were selected, the floodable surface increased, as expected, with the increasing rainfall intensity and duration of the simulation. With sufficient infiltration, only a portion of the water tends to stagnate and flow off on the surface toward the outlet. A sensitivity analysis of certain parameters, such as rainfall data and the final infiltration coefficient in the lower watershed of the littoral region, was conducted; the results show that the model simulates well the general character of water flow in the watershed. Finally, the model’s validation using field-collected parameters during the flood of 25 July 2017 and 18 to 22 July 2016 in the Grand Ouaga basin in Burkina reveals Nash–Sutcliffe values of 0.7 and 0.73, respectively. Full article

(This article belongs to the Topic Fluid Mechanics)

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29 pages, 5065 KiB  

Open AccessArticle

Software for Monitoring the In-Service Efficiency of Hydraulic Pumps

by Alin-Adrian Anton, Adrian Cococeanu and Sebastian Muntean

Appl. Sci. 2022, 12(22), 11450; https://0-doi-org.brum.beds.ac.uk/10.3390/app122211450 - 11 Nov 2022

Cited by 2 | Viewed by 1493

Abstract

The present paper introduces the creation of an algorithm and the software used to determine the energetic performance and monitor the efficiency of hydraulic pumps working in various industrial applications, such as water supply systems, water treatment processes, and irrigation systems, particularly in [...] Read more.

The present paper introduces the creation of an algorithm and the software used to determine the energetic performance and monitor the efficiency of hydraulic pumps working in various industrial applications, such as water supply systems, water treatment processes, and irrigation systems, particularly in the cases where there is no permanent monitoring. Our field investigations and the surveyed literature show that the only parameter that is neither monitored nor computed is the efficiency of the pumps. The software implementation allows for determining the in-service efficiency of the pumps and comparing it to the value associated with the best efficiency point (BEP). The solution is user-friendly and can be easily installed on any computer or smartphone. The software has been applied and tested in the Hydraulic Machines Laboratory at the “Politehnica” University Timişoara and at the AQUATIM S.A. regional water supply company. The software module monitors the operating regimes of the pumps and supports the deployment of predictive maintenance and servicing. Full article

(This article belongs to the Topic Fluid Mechanics)

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12 pages, 4704 KiB  

Open AccessArticle

Modeling and Experimental Study of the Dual Cylinder Fluid Inerter

by Fu Du, Chao Wang and Wei Nie

Appl. Sci. 2022, 12(21), 10849; https://0-doi-org.brum.beds.ac.uk/10.3390/app122110849 - 26 Oct 2022

Viewed by 1025

Abstract

The fluid inerter is a new mechanical element which has received great attention in the field of vibration reduction. However, due to the influence of secondary flow in the curved channel, the damping force is too large and the inertia force is relatively [...] Read more.

The fluid inerter is a new mechanical element which has received great attention in the field of vibration reduction. However, due to the influence of secondary flow in the curved channel, the damping force is too large and the inertia force is relatively small, which limits the engineering applications of the single-cylinder fluid inerter. To eliminate the influence of secondary flow in the single-cylinder fluid inerter, this paper proposes a dual-cylinder fluid inerter that has a straight tube instead of the spiral pipe or spiral groove. We Analyze the working principle, derive conditions of free movement, establish the damping force and inertia force model, and prove the validity of the model through bench testing. Contrastingly, it is found that the maximum parasitic damping force is only 40.32% of the single-cylinder structure, but the inertia force increases to 180.96% of the single-cylinder structure. The proposed inerter greatly increases the proportion of inertia force, and provides a new scheme for engineering applications. Full article

(This article belongs to the Topic Fluid Mechanics)

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20 pages, 17838 KiB  

Open AccessArticle

Numerical Study on Single-Bubble Contraction–Rebound Characteristics in Cryogenic Fluids

by Shaohang Yan, Tianwei Lai, Qi Zhao, Mingchen Qiang, Mingzhe Liu, Wenjing Ding, Yutao Liu and Yu Hou

Appl. Sci. 2022, 12(21), 10839; https://0-doi-org.brum.beds.ac.uk/10.3390/app122110839 - 26 Oct 2022

Viewed by 942

Abstract

In cryogenic fluid storage and delivery, the rapid contraction and rebound of bubbles are prone to occur during bubble collapse due to the pressure saltation. With the contraction and rebound of bubbles, the pressure and temperature in the bubbles fluctuate greatly, which affects [...] Read more.

In cryogenic fluid storage and delivery, the rapid contraction and rebound of bubbles are prone to occur during bubble collapse due to the pressure saltation. With the contraction and rebound of bubbles, the pressure and temperature in the bubbles fluctuate greatly, which affects the service life of fluid machinery. During bubble contraction and rebound, there is an accompanied complex heat and mass transfer process. According to the thermal properties of cryogenic fluids, a single-bubble collapse model is proposed considering the temperature variations inside the bubble. In order to study the variation in temperature and pressure during bubble collapse in cryogenic fluids, the contraction and rebound of a single bubble in liquid hydrogen are investigated numerically under various operating pressures and supercooling degrees. The numerical results of the model indicate that there are periodic contraction and rebound of the bubble when the pressure rises suddenly. Furthermore, the periods and attenuation rates of bubbles in different media are studied and compared. For the most concerned pressure and temperature characteristics, the relationship between the peak pressure, the attenuation rate of the temperature and the dimensionless number is proposed. Full article

(This article belongs to the Topic Fluid Mechanics)

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23 pages, 1611 KiB  

Open AccessArticle

The Modified Local Boundary Knots Method for Solution of the Two-Dimensional Advection–Diffusion Equation

by Karel Kovářík and Juraj Mužík

Mathematics 2022, 10(20), 3855; https://0-doi-org.brum.beds.ac.uk/10.3390/math10203855 - 18 Oct 2022

Cited by 1 | Viewed by 1152

Abstract

This paper deals with a new modification of the local boundary knots method (LBKM), which will allow the irregular node distribution and the arbitrary shape of the solution domain. Unlike previous localizations, it has no requirements on the number of nodes in the [...] Read more.

This paper deals with a new modification of the local boundary knots method (LBKM), which will allow the irregular node distribution and the arbitrary shape of the solution domain. Unlike previous localizations, it has no requirements on the number of nodes in the support or on the number of virtual points. Owing to the limited number of virtual points, the condition number of boundary knots matrix remains relatively low. The article contains the derivation of the relations of the method for steady and unsteady states and shows its effectiveness in three control examples. Full article

(This article belongs to the Topic Fluid Mechanics)

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16 pages, 5998 KiB  

Open AccessArticle

Accelerated Parallel Numerical Simulation of Large-Scale Nuclear Reactor Thermal Hydraulic Models by Renumbering Methods

by Huajian Zhang, Xiao-Wei Guo, Chao Li, Qiao Liu, Hanwen Xu and Jie Liu

Appl. Sci. 2022, 12(20), 10193; https://0-doi-org.brum.beds.ac.uk/10.3390/app122010193 - 11 Oct 2022

Cited by 1 | Viewed by 1097

Abstract

Numerical simulation of thermal hydraulics of nuclear reactors is widely concerned, but large-scale fluid simulation is still prohibited due to the complexity of components and huge computational effort. Some applications of open source CFD programs still have a large gap in terms of [...] Read more.

Numerical simulation of thermal hydraulics of nuclear reactors is widely concerned, but large-scale fluid simulation is still prohibited due to the complexity of components and huge computational effort. Some applications of open source CFD programs still have a large gap in terms of comprehensiveness of physical models, computational accuracy and computational efficiency compared with commercial CFD programs. Therefore, it is necessary to improve the computational performance of in-house CFD software (YHACT, the parallel analysis code of thermohydraulices) to obtain the processing capability of large-scale mesh data and better parallel efficiency. In this paper, we will form a unified framework of meshing and mesh renumbering for solving fluid dynamics problems with unstructured meshes. Meanwhile, the effective Greedy, RCM (reverse Cuthill-Mckee), and CQ (cell quotient) grid renumbering algorithms are integrated into YHACT software. An important judgment metric, named median point average distance (MDMP), is applied as the discriminant of sparse matrix quality to select the renumbering methods with better effect for different physical models. Finally, a parallel test of the turbulence model with 39.5 million grid volumes is performed using a pressurized water reactor engineering case component with 3*3 rod bundles. The computational results before and after renumbering are also compared to verify the robustness of the program. Experiments show that the CFD framework integrated in this paper can correctly perform simulations of the thermal engineering hydraulics of large nuclear reactors. The parallel size of the program reaches a maximum of 3072 processes. The renumbering acceleration effect reaches its maximum at a parallel scale of 1536 processes, 56.72%. It provides a basis for our future implementation of open-source CFD software that supports efficient large-scale parallel simulations. Full article

(This article belongs to the Topic Fluid Mechanics)

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21 pages, 6618 KiB  

Open AccessArticle

Effect of Multistage Circulation Control on Blade Aerodynamic Performance

by Hai Du, Lejie Yang, Shuo Chen, Wenxiao Zhang and Shengchun Han

Energies 2022, 15(19), 7395; https://0-doi-org.brum.beds.ac.uk/10.3390/en15197395 - 09 Oct 2022

Viewed by 1286

Abstract

To improve the low aerodynamic efficiency and reduce the high energy consumption of a single-stage circulation control wing, a multistage circulation control wing was designed. By combining force measurement and particle image velocimetry (PIV), the aerodynamic and flow-field characteristics of an aerofoil were [...] Read more.

To improve the low aerodynamic efficiency and reduce the high energy consumption of a single-stage circulation control wing, a multistage circulation control wing was designed. By combining force measurement and particle image velocimetry (PIV), the aerodynamic and flow-field characteristics of an aerofoil were investigated with respect to the increase in the number of blowing slots, changes in the blowing coefficient, and different blowing ratios for three slots. The force measurement results revealed that the maximum lift-to-drag ratio resulting from simultaneous blowing into the three slots increased by 95.3% compared with that in the absence of circulation control. With an increase in the blowing coefficient, two stages were observed: separation control and supercirculation control. In the separation control stage, the lift and drag coefficients significantly increased and decreased, respectively. In the supercirculation control stage, the lift coefficient gradually increased with the blowing coefficient, whereas the drag coefficient remained unchanged. When the blowing ratio (blowing flow ratio of three slots) in the three slots was 3:1:2, the maximum lift-to-drag ratio of the wing could reach 143.48%. The effects of different slot positions on the aerodynamic control were found to vary. The effects of Slot.1 and Slot.3 in terms of the drag reduction and lift, respectively, were evident, and the influence of Slot.2 on blowing between these two slots played a role in jet relay. The PIV results revealed that multistage blowing circulation increased the curvature of the trailing-edge streamline, thus increasing the equivalent aerofoil camber and improving the wing lift. At a high angle of attack, this circulation demonstrated a flow separation control effect. Full article

(This article belongs to the Topic Fluid Mechanics)

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14 pages, 4348 KiB  

Open AccessArticle

Instability of Viscoelastic Liquid Sheets in a Transverse Electric Field

by Lu Niu and Xiangdong Deng

Mathematics 2022, 10(19), 3488; https://0-doi-org.brum.beds.ac.uk/10.3390/math10193488 - 24 Sep 2022

Viewed by 939

Abstract

The temporal linear instability of a viscoelastic liquid sheet moving around an inviscid gas in a transverse electrical field is analyzed. The fluid is described by the leaky dielectric model, which is more complex than existing models and enables a characterization of the [...] Read more.

The temporal linear instability of a viscoelastic liquid sheet moving around an inviscid gas in a transverse electrical field is analyzed. The fluid is described by the leaky dielectric model, which is more complex than existing models and enables a characterization of the liquid electrical properties. In addition, the liquid is assumed to be viscoelastic, and the dimensionless dispersion relation of the sinuous and varicose modes between the wavenumber and the temporal growth rate can be derived as a 3 × 3 matrix. According to this relationship, the effects of the liquid properties on the sheet instability are determined. The results suggest that, as the electrical Euler number and the elasticity number increase and the time constant ratio decreases, the sheet becomes more unstable. Finally, an energy budget approach is adopted to investigate the instability mechanism for the sinuous mode. Full article

(This article belongs to the Topic Fluid Mechanics)

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21 pages, 17193 KiB  

Open AccessArticle

Numerical and Field Investigations of Acoustic Emission Laws of Coal Fracture under Hydro-Mechanical Coupling Loading

by Jie-Fang Song, Cai-Ping Lu, Zhao-Wei Zhan, Hai-Feng Cui, Yan-Min Wang and Jian-Hua Wang

Materials 2022, 15(19), 6510; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15196510 - 20 Sep 2022

Cited by 3 | Viewed by 1353

Abstract

Taking coal under hydro-mechanical coupling as the research object, the discrete element software PFC3D (particle flow code) was used to analyze the relationships among the force, acoustic emission (AE), and energy during coal fracture. Based on the moment tensor (MT) inversion, we revealed [...] Read more.

Taking coal under hydro-mechanical coupling as the research object, the discrete element software PFC3D (particle flow code) was used to analyze the relationships among the force, acoustic emission (AE), and energy during coal fracture. Based on the moment tensor (MT) inversion, we revealed the AE event distribution and source type during crack initiation and propagation until the final failure of coal. Meanwhile, we examined the relationships among the stress, number and type of cracks, magnitude, K_E, and b value of AE under different water and confining pressures. The results show that the numerical simulation can effectively determine the microscopic damage mechanism of coal under different conditions. Moreover, the rupture type of the numerical simulation is consistent with the field investigations, which verifies the rationality of the simulation. These research results can provide reference for safety production evaluation of water inrush mines. Full article

(This article belongs to the Topic Fluid Mechanics)

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12 pages, 1791 KiB  

Open AccessArticle

Performance of Textile Mask Materials in Varied Humidity: Filtration Efficiency, Breathability, and Quality Factor

by Joelle M. Segovia, Ching-Hsuan Huang, Maxwell Mamishev, Nanhsun Yuan, Jiayang He and Igor Novosselov

Appl. Sci. 2022, 12(18), 9360; https://0-doi-org.brum.beds.ac.uk/10.3390/app12189360 - 18 Sep 2022

Cited by 3 | Viewed by 2172

Abstract

During the COVID-19 pandemic, reusable masks became ubiquitous; these masks were made from various fabrics without guidance from the research community or regulating agencies. Though reusable masks reduce the waste stream associated with disposable masks and promote the use of masks by the [...] Read more.

During the COVID-19 pandemic, reusable masks became ubiquitous; these masks were made from various fabrics without guidance from the research community or regulating agencies. Though reusable masks reduce the waste stream associated with disposable masks and promote the use of masks by the population, their efficacy in preventing the transmission of infectious agents has not been evaluated sufficiently. Among the unknowns is the effect of relative humidity (RH) on fabrics’ filtration efficiency (FE) and breathability. This study evaluates the FE and breathability of several readily accessible mask materials in an aerosol chamber. Sodium chloride aerosols were used as the challenge aerosol with aerodynamic particle diameter in the 0.5 to 2.5 µm range. To mimic the variability in RH in the environment and the exhaled-breath condition, the chamber was operated at RH of 30% to 70%. The face velocity was varied between 0.05 m/s and 0.19 m/s to simulate different breathing rates. The FE and pressure drop were used to determine the quality factor of the materials. Among the tested materials, the 3M P100 filter has the highest pressure drop of 140 Pa; the N95 mask and the 3M P100 have almost 100% FE for all sizes of particles and tested face velocities; the surgical mask has nearly 90% FE for all the particles and the lowest pressure drop among the certified materials, which ranks it the second to the N95 mask in the quality factor. Other material performance data are presented as a function of relative humidity and aerosol size. The quality factor for each material was compared against reference filtration media and surgical masks. Multiple layers of selected materials are also tested. While the additional layers improve FE, the pressure drop increases linearly. Additionally, the certified materials performed approximately three times better than the highest performing non-certified material. Full article

(This article belongs to the Topic Fluid Mechanics)

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14 pages, 3841 KiB  

Open AccessArticle

Numerical Study on the Effect of Deposit Layer on the Minimum Wall Thickness of Boiler Water Tube under Different Operating Conditions

by Ahmed S. Aljohani, Khaled I. Ahmed, Saeed Asiri and Mohamed H. Ahmed

Appl. Sci. 2022, 12(17), 8838; https://0-doi-org.brum.beds.ac.uk/10.3390/app12178838 - 02 Sep 2022

Cited by 2 | Viewed by 1582

Abstract

Water wall tube temperature is a major parameter in the steam generator design which has a significant role in keeping the steam generator available. Thus, knowing the tube average temperature in different operating conditions is very important to avoid the causes of tube [...] Read more.

Water wall tube temperature is a major parameter in the steam generator design which has a significant role in keeping the steam generator available. Thus, knowing the tube average temperature in different operating conditions is very important to avoid the causes of tube failures. High temperatures are a major cause of various types of failures, such as overheating, hydrogen damage, thermal stress, etc. Furthermore, deposits on the inner tube wall contribute to such failure by changing the thermal resistance of the tube wall, which causes a significant increase in the tube wall’s average temperature, consequently lowering the allowable stress. Therefore, the model was created by using ANSYS FLUENT (Canonsburg, PA, USA) to determine the wall average water tube wall temperature considering the deposit layer thickness (magnetite). Furthermore, this model was verified. It was found that increasing tube thickness can increase the average tube temperature but combining it with increasing deposit thickness leads to higher temperatures. In other words, the effect of the deposit on the tube with higher thickness is higher than on the tube with lower thickness. By discussing the minimum thickness of the water wall tube, the suitable selection of the tube thickness and courses of action concerning the operating conditions that minimize the potential overheating of water tubes in the furnace section of the boiler can be determined. Full article

(This article belongs to the Topic Fluid Mechanics)

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16 pages, 6497 KiB  

Open AccessArticle

Two-Phase Flow of Eyring–Powell Fluid with Temperature Dependent Viscosity over a Vertical Stretching Sheet

by Ahlam Aljabali, Abdul Rahman Mohd Kasim, Nur Syamilah Arifin, Noor Amalina Nisa Ariffin, Dennis Ling Chuan Ching, Iskandar Waini, Najiyah Safwa Khashi’ie and Nurul Amira Zainal

Mathematics 2022, 10(17), 3111; https://0-doi-org.brum.beds.ac.uk/10.3390/math10173111 - 30 Aug 2022

Cited by 4 | Viewed by 1155

Abstract

In this work, the mixed convection flow of non-Newtonian Eyring–Powell fluid with the effects of temperature dependent viscosity (TDV) were studied together with the interaction of dust particles under the influence of Newtonian Heating (NH) boundary condition, which assume to move over a [...] Read more.

In this work, the mixed convection flow of non-Newtonian Eyring–Powell fluid with the effects of temperature dependent viscosity (TDV) were studied together with the interaction of dust particles under the influence of Newtonian Heating (NH) boundary condition, which assume to move over a vertical stretching sheet. Alternatively, the dusty fluid model was categorized as a two-phase flow that consists of phases of fluid and dust. Through the use of similarity transformations, governing equations of fluid and dust phases are reduced into ordinary differential equations (ODE), then solved by efficient numerical Keller–box method. Numerical solution and asymptotic results for limiting cases will be presented to investigate how the flow develops at the leading edge and its end behaviour. Comparison with the published outputs in literature evidence verified the precision of the present results. Graphical diagrams presenting velocity and temperature profiles (fluid and dust) were conversed for different influential parameters. The effects of skin friction and heat transfer rate were also evaluated. The discovery indicates that the presence of the dust particles have an effect on the fluid motion, which led to a deceleration in the fluid transference. The present flow model can match to the single phase fluid cases if the fluid particle interaction parameter is ignored. The fluid velocity and temperature distributions are always higher than dust particles, besides, the opposite trend between both phases is noticed with $\beta$. Meanwhile, both phases share the similar trend in conjunction with the rest factors. Almost all of the temperature profiles are not showing a significant change, since the viscosity of fluid is high, which can be perceived in the figures. Furthermore, the present study extends some theoretical knowledge of two-phase flow. Full article

(This article belongs to the Topic Fluid Mechanics)

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14 pages, 4871 KiB  

Open AccessArticle

Hydrodynamic Characteristics of Two Side-by-Side Cylinders at a Pitch Ratio of 2 at Low Subcritical Reynolds Numbers

by Thiago Gomes, Jhon Goulart and Carla Anflor

Fluids 2022, 7(9), 287; https://0-doi-org.brum.beds.ac.uk/10.3390/fluids7090287 - 30 Aug 2022

Viewed by 1522

Abstract

Isothermal turbulent flow around circular cylinders arranged side-by-side was numerically simulated on a commercial finite-volumes platform, ANSYS^® CFX, version 2020 R2. The turbulence was modeled by using k-ω shear stress transport (k-ω SST). Three different Reynolds numbers were computed, Re_d [...] Read more.

Isothermal turbulent flow around circular cylinders arranged side-by-side was numerically simulated on a commercial finite-volumes platform, ANSYS^® CFX, version 2020 R2. The turbulence was modeled by using k-ω shear stress transport (k-ω SST). Three different Reynolds numbers were computed, Re_d = 200, 1000, and 3000, which were based on the cylinder diameter, d, the free stream velocity, U∞, and the kinematic viscosity of the fluid, ν. Sided cylinders were spaced apart from each other, forming a p/d ratio equal to 2, which was kept constant throughout the computations regardless of changes in the Reynolds number. The drag coefficient, C_d, as well as its time traces, was evaluated along with the different wake topologies experienced by the cylinders (wide wake WW and narrow wake NW). The simulations were able to predict the bistable flow over the cylinders and the Cd changes associated with the wakes. Whenever a new wake topology was identified, the shape drag changed in accordance with the instantaneous pressure distribution. A laminar simulation was carried out for the lowest Reynolds number case, showing that the adopted turbulence model did not affect the dynamic response of the flow. The Re_d = 3000 case was compared to Afgan’s outcomes, whose simulations were carried out in a 3-D mesh using LES (Large Eddy Simulation), showing great agreement with their results. Full article

(This article belongs to the Topic Fluid Mechanics)

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16 pages, 8508 KiB  

Open AccessArticle

Intake System Performance Stability as a Function of Flow Throttling

by Adam Kozakiewicz, Stanisław Kachel, Michał Frant and Maciej Majcher

Energies 2022, 15(17), 6291; https://0-doi-org.brum.beds.ac.uk/10.3390/en15176291 - 29 Aug 2022

Viewed by 1360

Abstract

This paper presents a numerical analysis of the stability of the flow parameters along the intake duct of an aircraft jet turbine engine. This problem has been investigated by many research teams and was included in the literature analysis. The unstable operation of [...] Read more.

This paper presents a numerical analysis of the stability of the flow parameters along the intake duct of an aircraft jet turbine engine. This problem has been investigated by many research teams and was included in the literature analysis. The unstable operation of a turbojet intake system can be the consequence of many adverse factors, including an intake vortex. The investigated intake system, due to its low location to the plane of the airport, is highly susceptible to the formation of an intake vortex. The phenomenon of an intake vortex can, in the worst-case scenario, result in the surging of the turbojet, and even engine stalling. This paper presents a developed model of the forward section of an aircraft, complete with its intake duct, and the method of its discretization. The intake-system model and numerical analysis were performed in Ansys Fluent. The flow parameters adopted for numerical simulations, under specific boundary conditions, corresponded to the operating conditions of the engine cooperating with the investigated intake system. The numerical calculations were performed assuming an air-pressure rise in the end section of the engine-intake system, reflecting the reduction in the pitch angle of the inlet stator blades of the fan. As a result, the pressure distributions in a significant cross section in the intake system were obtained. The results were analyzed with the quantitative distribution of the pressure fields by applying a dimensionless potential-pressure ratio. The pressure ratio enabled a comparative analysis of the nonuniformity of the total-pressure distribution in selected cross sections of the intake system. The results were revealing in terms of growing unstable flows in the flow duct. A major conclusion drawn from the results, by testing the dimensionless potential-pressure ratio, was that, within certain limits, it was possible to improve the flow uniformity by increasing the throttling pressure. Full article

(This article belongs to the Topic Fluid Mechanics)

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20 pages, 2597 KiB  

Open AccessArticle

Different Modes of Combustion Wave on a Lattice Burner

by Vasily B. Novozhilov, Boris V. Lidskii and Vladimir S. Posvyanskii

Mathematics 2022, 10(15), 2731; https://0-doi-org.brum.beds.ac.uk/10.3390/math10152731 - 02 Aug 2022

Viewed by 1035

Abstract

The stabilization of a planar premixed flame front on a lattice (porous) burner is considered. The developed model captures all the important features of the phenomenon, while also admitting qualitative analytical investigation. It has been rigorously mathematically proven that there exist two different [...] Read more.

The stabilization of a planar premixed flame front on a lattice (porous) burner is considered. The developed model captures all the important features of the phenomenon, while also admitting qualitative analytical investigation. It has been rigorously mathematically proven that there exist two different stabilization regimes: one with flame front located nearby the surface of the burner, and another with the flame front located inside the lattice. These two regimes result in qualitatively different gas temperature profiles along the flow that is monotonic and non-monotonic, respectively. The boundary between the two regimes is described in terms of dependence of the lattice solid material temperature on flow Peclet number. With similar temperature profiles, such dependencies may be both monotonic and non-monotonic. The transition between the two types of dependencies is controlled by the Arrhenius number. Conclusions of the study are supported by numerical analysis. They also compare favorably with the available experimental data. The novelty of the present approach is a fundamentally rigorous analytical analysis of the problem. The proposed analytical model, based on $\delta$-function approximation of the chemical source term, agrees well (within 7% relative error) with the model based on the distributed description of the chemical reaction zone. The obtained results are important from both a theoretical and practical point of view. They demonstrate the existence of the two qualitatively different operating regimes for lattice burners, thus impacting design solutions for such devices. The results will be of great interest to the broader academic community, particularly in research areas where similar wave structures may emerge. Full article

(This article belongs to the Topic Fluid Mechanics)

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20 pages, 10854 KiB  

Open AccessArticle

Experimental Investigation on Jet Vector Deflection Jumping Phenomenon of Coanda Effect Nozzle

by Shaoqing Chi and Yunsong Gu

Appl. Sci. 2022, 12(15), 7567; https://0-doi-org.brum.beds.ac.uk/10.3390/app12157567 - 27 Jul 2022

Cited by 1 | Viewed by 1857

Abstract

The Coanda effect nozzle is a fluid thrust vectoring technology that uses the Coanda effect to control jet vector deflection. The jumping phenomenon often occurs in the process of controlling jet vector deflection. This phenomenon leads to the nonlinearity of thrust vector control. [...] Read more.

The Coanda effect nozzle is a fluid thrust vectoring technology that uses the Coanda effect to control jet vector deflection. The jumping phenomenon often occurs in the process of controlling jet vector deflection. This phenomenon leads to the nonlinearity of thrust vector control. It destroys the control performance of the aircraft and brings potential dangers to the safety of the aircraft. The jumping phenomenon occurs in an unsteady flow field different from the traditional flow phenomenon. The flow structure in an unsteady flow field changes with time, so it is not easy to control by the traditional active flow control method. This paper explains the reasons for the jumping phenomenon from two aspects: flow field stability and flow structure. Secondly, the unsteady flow field with the jumping phenomenon is studied and analyzed by a flow visualization experiment and dynamic force measurement. Furthermore, the dynamic modal decomposition (DMD) method is used to extract the characteristic frequencies of the critical vortices causing jets to jump in unsteady flow fields. Finally, a pulsed jet with the same characteristic frequency is used to control the varying vortices in the unsteady flow field. The experimental results show that the active flow control method, which extracts the characteristic frequency of the critical flow field structure by DMD, effectively suppresses the jumping phenomenon in the unsteady flow field. It also linearizes the process of jet nonlinear vector deflection. Full article

(This article belongs to the Topic Fluid Mechanics)

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26 pages, 7467 KiB  

Open AccessArticle

Hydrodynamic Impacts of Short Laser Pulses on Plasmas

by Gaetano Fiore, Monica De Angelis, Renato Fedele, Gabriele Guerriero and Dušan Jovanović

Mathematics 2022, 10(15), 2622; https://0-doi-org.brum.beds.ac.uk/10.3390/math10152622 - 27 Jul 2022

Cited by 3 | Viewed by 1029

Abstract

We determine conditions allowing for simplification of the description of the impact of a short and arbitrarily intense laser pulse onto a cold plasma at rest. If both the initial plasma density and pulse profile have plane symmetry, then suitable matched upper bounds [...] Read more.

We determine conditions allowing for simplification of the description of the impact of a short and arbitrarily intense laser pulse onto a cold plasma at rest. If both the initial plasma density and pulse profile have plane symmetry, then suitable matched upper bounds on the maximum and the relative variations of the initial density, as well as on the intensity and duration of the pulse, ensure a strictly hydrodynamic evolution of the electron fluid without wave-breaking or vacuum-heating during its whole interaction with the pulse, while ions can be regarded as immobile. We use a recently developed fully relativistic plane model whereby the system of the Lorentz–Maxwell and continuity PDEs is reduced into a family of highly nonlinear but decoupled systems of non-autonomous Hamilton equations with one degree of freedom, the light-like coordinate $\xi =ct-z$ instead of time t as an independent variable, and new a priori estimates (eased by use of a Liapunov function) of the solutions in terms of the input data (i.e., the initial density and pulse profile). If the laser spot radius R is finite and is not too small, the same conclusions hold for the part of the plasma close to the axis $\overrightarrow{z}$ of cylindrical symmetry. These results may help in drastically simplifying the study of extreme acceleration mechanisms of electrons. Full article

(This article belongs to the Topic Fluid Mechanics)

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10 pages, 2468 KiB  

Open AccessBrief Report

Model for Wall Shear Stress from Obliquely Impinging Planar Underexpanded Jets

by Patrick Fillingham, Arjun Viswanathan and Igor V. Novosselov

Appl. Sci. 2022, 12(14), 7311; https://0-doi-org.brum.beds.ac.uk/10.3390/app12147311 - 21 Jul 2022

Cited by 2 | Viewed by 1440

Abstract

Though inclined under-expanded planar jets are used in many practical applications, the wall stress resulting from their impingement has not been adequately characterized. Reduced-order models for wall shear as a function of jet parameters have not been reported. This work uses computational fluid [...] Read more.

Though inclined under-expanded planar jets are used in many practical applications, the wall stress resulting from their impingement has not been adequately characterized. Reduced-order models for wall shear as a function of jet parameters have not been reported. This work uses computational fluid dynamics to determine wall shear stress as a function of the nozzle parameters and jet angle. The simulations of the impinging jet are validated against the experimental data and direct numerical simulation; then, the jet parameters are varied to formulate an empirical relationship for maximum wall shear stress as a function of a nozzle pressure ratio, standoff distance, jet Reynolds number, and impingement angle. The global expression for shear stress agrees with the numerical results within a mean deviation of 3%. The relationship can be used for applications where shear stress information is required to design or assess the performance of practical systems, such as surface cleaning, particle resuspension from the surface, and surface cooling. Full article

(This article belongs to the Topic Fluid Mechanics)

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23 pages, 1089 KiB  

Open AccessArticle

Electrohydrodynamic Liquid Sheet Instability of Moving Viscoelastic Couple-Stress Dielectric Fluid Surrounded by an Inviscid Gas through Porous Medium

by Mohamed Fahmy El-Sayed and Agaeb Mahal Alanzi

Fluids 2022, 7(7), 247; https://0-doi-org.brum.beds.ac.uk/10.3390/fluids7070247 - 18 Jul 2022

Cited by 1 | Viewed by 1570

Abstract

Viscoelastic liquid sheet of couple-stress type streaming with relative motion into an inviscid gas through porous molium is studied theoretically and quantitatively in this project. To derive the differential equations that describe liquids, gases, and the electric field, we linearized the governing equations [...] Read more.

Viscoelastic liquid sheet of couple-stress type streaming with relative motion into an inviscid gas through porous molium is studied theoretically and quantitatively in this project. To derive the differential equations that describe liquids, gases, and the electric field, we linearized the governing equations of motion and continuity, Maxwell’s equations in quasi-static approximation, and the appropriate boundary conditions at the two interfaces. Then we used the normal mode method. It was demonstrated analytically that the solutions to these differential equations can be found for both symmetric and antisymmetric disturbances, respectively. We could not obtain an explicit form of the growth rates since we could not solve the dispersion relations for both situations because they were obtained in highly complex forms. The Mathematica program is used to solve the dimensionless forms of the dispersion relations numerically using Gaster’s theorem. Various influences on the stability analysis of the considered system have been studied in detail, and it is determined that the system in the presence of a porous material is more unstable than it would be otherwise. In a two-dimensional system, the antisymmetric disturbance case is found to be more unstable than the corresponding symmetric disturbance situation. Some characteristics, such as Wabe number, Ohnesorge number, and electric field, have destabilizing effects, whereas others, such as porosity, medium permeability, viscoelasticity parameter, gas-to-liquid viscosity ratio, and dielachic constants, have stabilizing effects. Finally, it is discovered that the gas-to-liquid velocity ratio plays a dual role in the stability condition depending on whether the gas-to-liquid velocity ratio U ≶ 1. In the past, we have only found evidence of very few previous studies. Full article

(This article belongs to the Topic Fluid Mechanics)

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14 pages, 2580 KiB  

Open AccessArticle

Thermographic Observation and Hydrodynamic Patterns of Inclined Ethanol Droplet Train Impingement on a Non-Uniformly Heated Glass Surface

by Baris Burak Kanbur, Sheng Quan Heng and Fei Duan

Fluids 2022, 7(7), 229; https://0-doi-org.brum.beds.ac.uk/10.3390/fluids7070229 - 07 Jul 2022

Cited by 1 | Viewed by 1370

Abstract

Droplet train impingement is a fundamental approach to mimic the complicated interactions between the fluid and the substrate in advanced thermal engineering applications in industry. Differently from previous studies, the main original contribution of this study is to perform an inclined droplet train [...] Read more.

Droplet train impingement is a fundamental approach to mimic the complicated interactions between the fluid and the substrate in advanced thermal engineering applications in industry. Differently from previous studies, the main original contribution of this study is to perform an inclined droplet train impingement on a non-uniformly heated surface. Ethanol was used as the liquid for droplet train impingement applications, while glass substrate was selected as the target surface. The inclined flow angle was 63 degrees. Both optical and thermographic observations were performed on the target surface by focusing on the droplet impact area. Three experimental sets were created with the Weber numbers 667.57, 841.90, and 998.01. A surface temperature range was selected between 85.00 °C and 200.00 °C, which was above the boiling point of the ethanol. The maximum spreading length was measured at 0.97 mm at the surface temperature of 82.00 °C for the experiment with the Weber number of 998.01, whilst the minimum spreading length was found at 0.18 mm at the highest surface temperature for the experiment with the Weber number of 667.57. A uniform splashing direction was observed above 170.00 °C for all experiments, which meant that the sign of the transition regime appeared. Full article

(This article belongs to the Topic Fluid Mechanics)

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24 pages, 9810 KiB  

Open AccessArticle

Effect of Leaching Behavior on the Geometric and Hydraulic Characteristics of Concrete Fracture

by Yuan Wang, Mengmeng Tao, Di Feng, Yu Jiao, Yulong Niu and Zhikui Wang

Materials 2022, 15(13), 4584; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15134584 - 29 Jun 2022

Cited by 2 | Viewed by 1374

Abstract

The leaching of material from concrete fracture surfaces has an impact on the structural concrete in service, but the number of studies that consider the effect of the coupling of the leaching, fracture geometry and hydraulic processes on concrete fractures is insufficient. In [...] Read more.

The leaching of material from concrete fracture surfaces has an impact on the structural concrete in service, but the number of studies that consider the effect of the coupling of the leaching, fracture geometry and hydraulic processes on concrete fractures is insufficient. In this study, a series of experiments was conducted, and a leaching model proposed, to investigate the mechanism of leaching behavior on the geometric and hydraulic characteristics of concrete fractures. Following the leaching experiment, the evolution of fracture geometric characteristics was observed by a three-dimensional (3D) laser scanning technique, finding that the fracture produces residual leached depth and local uneven leaching, which results in a decrease in roughness. The hydraulic characteristics were then investigated by permeability tests, and it was found that the fracture hydraulic aperture and permeability increase monotonically with leaching time. A simulation of fluid flow in a numerical fracture revealed the effect of residual leached depth and a decrease in roughness on the hydraulic characteristics. Finally, based on the analysis of the chemical composition of the leaching solution, a leaching model of concrete rough fracture surface is proposed and the mechanism of leaching behavior is discussed. These new findings are useful for the understanding of the development of leaching, local to concrete fracture surfaces. Full article

(This article belongs to the Topic Fluid Mechanics)

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14 pages, 2174 KiB  

Open AccessArticle

Free Energy Changes during Spherical Droplet Deposition—Mechanistic Model

by Jacek A. Michalski and Slawomir Jakiela

Energies 2022, 15(13), 4725; https://0-doi-org.brum.beds.ac.uk/10.3390/en15134725 - 28 Jun 2022

Viewed by 1103

Abstract

On the basis of theoretical considerations (mechanistic model), an equation was determined that allowed to calculate the free energy (Helmholtz) of a spherical droplet deposited on a flat surface in a system without external forces. Assuming isochoric and isothermal transformation of the system [...] Read more.

On the basis of theoretical considerations (mechanistic model), an equation was determined that allowed to calculate the free energy (Helmholtz) of a spherical droplet deposited on a flat surface in a system without external forces. Assuming isochoric and isothermal transformation of the system and a very fast conversion of mechanical energy into heat, the obtained equation allows to determine the trajectory of thermodynamic transformation consisting of the spreading of the droplet on the surface of the substrate. The similarities and differences in the behaviour of spherical droplets described by the mechanistic model and Young’s model, together with its improvements, were discussed. The trajectories of free energy changes during the spreading of droplets in a system in which the adhesive force acting perpendicular to the wetted surface was considered as well. Full article

(This article belongs to the Topic Fluid Mechanics)

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21 pages, 4906 KiB  

Open AccessArticle

Insight in Thermally Radiative Cilia-Driven Flow of Electrically Conducting Non-Newtonian Jeffrey Fluid under the Influence of Induced Magnetic Field

by Fehid Ishtiaq, Rahmat Ellahi, Muhammad Mubashir Bhatti and Sultan Z. Alamri

Mathematics 2022, 10(12), 2007; https://0-doi-org.brum.beds.ac.uk/10.3390/math10122007 - 10 Jun 2022

Cited by 48 | Viewed by 1979

Abstract

This paper investigates the mobility of cilia in a non-uniform tapered channel in the presence of an induced magnetic field and heat transfer. Thermal radiation effects are included in the heat transfer analysis. The Jeffrey model is a simpler linear model that uses [...] Read more.

This paper investigates the mobility of cilia in a non-uniform tapered channel in the presence of an induced magnetic field and heat transfer. Thermal radiation effects are included in the heat transfer analysis. The Jeffrey model is a simpler linear model that uses time derivatives rather than convected derivatives as the Oldroyd-B model does; it depicts rheology other than Newtonian. The Jeffrey fluid model is used to investigate the rheology of a fluid with cilia motion. The proposed model examines the behavior of physiological fluids passing through non-uniform channels, which is responsible for symmetrical wave propagation and is commonly perceived between the contraction and expansion of concentric muscles. To formulate the mathematical modeling, the lubrication approach is used for momentum, energy, and magnetic field equations. The formulated linear but coupled differential equations have been solved analytically. Graphs for velocity profile, magnetic force function, induced magnetic field, current density, pressure rise, and heat profile are presented to describe the physical mechanisms of significant parameters. It is found that the eccentricity parameter of the cilia equations opposes the velocity and the magnetic force functions. The thermal radiation decreases the temperature profile while it increases for Prandtl and Eckert numbers. A promising impact of the magnetic Reynolds number and electric field on the current density profile is also observed. Full article

(This article belongs to the Topic Fluid Mechanics)

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19 pages, 5547 KiB  

Open AccessArticle

Mathematical Modeling of Sintering Air Leakage through Holes

by Jin Cai, Xiangwei Kong and Mingzhu Yu

Energies 2022, 15(12), 4224; https://0-doi-org.brum.beds.ac.uk/10.3390/en15124224 - 08 Jun 2022

Cited by 1 | Viewed by 1821

Abstract

The air leakage in sintering machines affects the technological and economic indexes of the sintering process. It is of great significance to monitor and estimate the key areas. Mathematical models of sintering air leakage through holes in the steady-state process are given based [...] Read more.

The air leakage in sintering machines affects the technological and economic indexes of the sintering process. It is of great significance to monitor and estimate the key areas. Mathematical models of sintering air leakage through holes in the steady-state process are given based on the fluid mechanics to predict the flow rate and effect on the key area. It was found that the hole model is the application of constant orifice outflow in the computation of sintering air leakage. The counter-flow bed model is suitable for predicting the flow rate through a complete break in sintering wind boxes. Furthermore, This paper proposes a new hole–bed generalized model to cover all the possible hole diameters for further high-precision application. The model connects the leakage hole diameter with the sintering process for the first time and establishes their coupling relationship. The pressure state in the sintering system depends on the ratio of the leakage hole area to the sintering bed area. The proposed fast estimation models are a step forward in developing more precise and powerful calculation tools to foresee the effects and consequences of sintering air leakage. It has a good prospect for reducing and replacing complex manual measurement and bringing some insight into the state of the art that could be improved in the future. Full article

(This article belongs to the Topic Fluid Mechanics)

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