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A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "A: Sustainable Energy".

Deadline for manuscript submissions: closed (31 January 2022) | Viewed by 30438

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Dr. Ziemowit Malecha

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Department of Cryogenic, Aeronautic and Process Engineering, Wroclaw University of Science and Technology, 50-370 Wroclaw, Poland
Interests: fluid mechanics; numerical methods; heat and mass transfer; cryogenics; aerodynamics; wind turbines
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Special Issue Information

Dear Colleagues,

We are pleased to announce a Special Issue of the journal Energies on the topic of Turbulence and Fluid Mechanics. We invite submissions related to experimental, numerical, and theoretical studies.

Although issues related to turbulence and fluid mechanics have been extensively studied for a very long time and many answers have been found, many problems are still open, and a number of new interesting issues are constantly emerging.

The current Special Issue welcomes papers related to turbulence, vortex structures, and vortex dynamics, scientific, and engineering problems where turbulence is of main importance, including multiphase flows and general fluid mechanics.

The purpose of this Special Issue is to collect a number of multidisciplinary problems linked by turbulence and fluid mechanics. We believe it would be very helpful for the community to find a new common ground for possible collaboration.

Prof. Dr. Ziemowit Malecha
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

Turbulence
Vortex structures
Vortex dynamics and interactions
hydro- and aerodynamics
Multiphase flow

Published Papers (12 papers)

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Editorial

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4 pages, 159 KiB

Open AccessEditorial

Turbulence and Fluid Mechanics

by Ziemowit Malecha

Energies 2022, 15(3), 1116; https://0-doi-org.brum.beds.ac.uk/10.3390/en15031116 - 02 Feb 2022

Cited by 2 | Viewed by 1198

Abstract

This Special Issue of Energies features 11 scientific papers on the subject of turbulence and fluid mechanics [...] Full article

(This article belongs to the Special Issue Turbulence and Fluid Mechanics)

Research

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21 pages, 3390 KiB

Open AccessArticle

Numerical Study of Baroclinic Acoustic Streaming Phenomenon for Various Flow Parameters

by Błażej Baran, Krystian Machaj, Ziemowit Malecha and Krzysztof Tomczuk

Energies 2022, 15(3), 854; https://0-doi-org.brum.beds.ac.uk/10.3390/en15030854 - 25 Jan 2022

Cited by 5 | Viewed by 2075

Abstract

The article presents a numerical study of the large-amplitude, acoustically-driven streaming flow for different frequencies of the acoustic wave and different temperature gradients between hot and cold surfaces. The geometries studied were mainly two-dimensional rectangular resonators of different lengths, but also one three-dimensional rectangular resonator and one long and narrow channel, representative of a typical U-shaped resistance thermometer. The applied numerical model was based on the Navier–Stokes compressible equations, the ideal gas model, and finite volume discretization. The oscillating wall of the considered geometries was modeled as a dynamically moving boundary of the numerical mesh. The length of the resonators was adjusted to one period of the acoustic wave. The research confirmed that baroclinic acoustic streaming flow was largely independent of frequency, and its intensity increased with the temperature gradient between the hot and cold surface. Interestingly, a slight maximum was observed for some oscillation frequencies. In the case of the long and narrow channel, acoustic streaming manifested itself as a long row of counter-rotating vortices that varied slightly along the channel. 3D calculations showed that a three-dimensional pair of streaming vortices had formed in the resonator. Examination of the flow in selected cross-sections showed that the intensity of streaming gradually decreased as it approached the side walls of the resonator creating a quasi-parabolic profile. The future development of the research will focus on fully 3D calculations and precise identification of the influence of the bounding walls on the streaming flow. Full article

(This article belongs to the Special Issue Turbulence and Fluid Mechanics)

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32 pages, 12416 KiB

Open AccessArticle

Vortex Trapping Cavity on Airfoil: High-Order Penalized Vortex Method Numerical Simulation and Water Tunnel Experimental Investigation

by Dominik Błoński, Katarzyna Strzelecka and Henryk Kudela

Energies 2021, 14(24), 8402; https://0-doi-org.brum.beds.ac.uk/10.3390/en14248402 - 13 Dec 2021

Cited by 8 | Viewed by 3108

Abstract

This paper presents a two-dimensional implementation of the high-order penalized vortex in cell method applied to solve the flow past an airfoil with a vortex trapping cavity operating under moderate Reynolds number. The purpose of this article is to investigate the fundamentals of the vortex trapping cavity. The first part of the paper treats with the numerical implementation of the method and high-order schemes incorporated into the algorithm. Poisson, stream-velocity, advection, and diffusion equations were solved. The derivation, finite difference formulation, Lagrangian particle remeshing procedure, and accuracy tests were shown. Flow past complex geometries was possible through the penalization method. A procedure description for preparing geometry data was included. The entire methodology was tested with flow past impulsively started cylinder for three Reynolds numbers: 550, 3000, 9500. Drag coefficient, streamlines, and vorticity contours were checked against results obtained by other authors. Afterwards, simulations and experimental results are presented for a standard airfoil and those equipped with a trapping vortex cavity. Airfoil with an optimized cavity shape was tested under three angles of attack: 3°, 6°, 9°. The Reynolds number is equal to Re = 2 × 10⁴. Apart from performing flow analysis, drag and lift coefficients for different shapes were measured to assess the effect of vortex trapping cavity on aerodynamic performance. Flow patterns were compared against ultraviolet dye visualizations obtained from the water tunnel experiment. Full article

(This article belongs to the Special Issue Turbulence and Fluid Mechanics)

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21 pages, 13339 KiB

Open AccessArticle

Surface Roughness Effects on Flows Past Two Circular Cylinders in Tandem Arrangement at Co-Shedding Regime

by Paulo Guimarães de Moraes and Luiz Antonio Alcântara Pereira

Energies 2021, 14(24), 8237; https://0-doi-org.brum.beds.ac.uk/10.3390/en14248237 - 07 Dec 2021

Cited by 13 | Viewed by 2526

Abstract

This paper contributes by investigating surface roughness effects on temporal history of aerodynamic loads and vortex shedding frequency of two circular cylinders in tandem arrangement. The pair of cylinders is immovable; of equal outer diameter, D; and its geometry is defined by the dimensionless center-to-center pitch ratio, L/D. Thus, a distance of L/D = 4.5 is chosen to characterize the co-shedding regime, where the two shear layers of opposite signals, originated from each cylinder surface, interact generating counter-rotating vortical structures. A subcritical Reynolds number of Re = 6.5 × 10⁴ is chosen for the test cases, which allows some comparisons with experimental results without roughness effects available in the literature. Two relative roughness heights are adopted, nominally ε/D = 0.001 and 0.007, aiming to capture the sensitivity of the applied numerical approach. Recent numerical results published in the literature have reported that the present two-dimensional model of surface roughness effects is able to capture both drag reduction and full cessation of vortex shedding for an immovable cylinder near a moving ground. That roughness model was successfully blended with a Lagrangian vortex method using sub-grid turbulence modeling. Overall, the effects of relative roughness heights on flows past two cylinders reveal changing of behavior of the vorticity dynamics, in which drag reduction, intermittence of vortex shedding, and wake destruction are identified under certain roughness effects. This kind of study is very useful for engineering conservative designs. The work is also motivated by scarcity of results previous discussing flows past cylinders in cross flow with surface roughness effects. Full article

(This article belongs to the Special Issue Turbulence and Fluid Mechanics)

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26 pages, 3631 KiB

Open AccessArticle

The Thermal—Flow Processes and Flow Pattern in a Pulsating Heat Pipe—Numerical Modelling and Experimental Validation

by Przemysław Błasiak, Marcin Opalski, Parthkumar Parmar, Cezary Czajkowski and Sławomir Pietrowicz

Energies 2021, 14(18), 5952; https://0-doi-org.brum.beds.ac.uk/10.3390/en14185952 - 19 Sep 2021

Cited by 15 | Viewed by 3518

Abstract

The aim of the article is to numerically model a two-dimensional multiphase flow based on the volume of fluid method (VOF) in a pulsating heat pipe (PHP). The current state of knowledge regarding the modeling of these devices was studied and summarised. The proposed model is developed within open source software, OpenFOAM, based on the predefined solver called interPhaseChangeFoam. The analyses were carried out in terms of the influence of four different mass transfer models between the phases, proposed by Tanasawa, Lee, Kafeel and Turan, and Xu et al. on the shape and dynamics of the internal flow structures. The numerical models were validated against data obtained from a specially designed experimental setup, consisting of three bends of pulsating heat pipes. The numerical calculations were carried out with ethanol being treated as a working medium and the initial and boundary conditions taken directly from the measurement procedures. The variable input parameter for the model was the heat flux implemented in the evaporation section and a fixed temperature applied to the condensation section. The flow structures obtained from the numerical analyses were compared and discussed with the flow structures gained from experimental studies by employing a high speed camera. In addition, to verify the quantitative results obtained from the numerical analyses with the experimental data, a technique called particle image velocimetry (PIV) was used for the velocity vector field. For the analysed velocity ranges, the relative error obtained was reached at the level of 10%. Full article

(This article belongs to the Special Issue Turbulence and Fluid Mechanics)

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19 pages, 5601 KiB

Open AccessArticle

Simplified Transition and Turbulence Modeling for Oscillatory Pipe Flows

by Alexander Shapiro, Gershon Grossman and David Greenblatt

Energies 2021, 14(5), 1410; https://0-doi-org.brum.beds.ac.uk/10.3390/en14051410 - 04 Mar 2021

Cited by 2 | Viewed by 1804

Abstract

One-dimensional unsteady Reynolds-averaged Navier–Stokes computations were performed for oscillatory transitional and turbulent pipe flows and the results were validated against existing experimental data for a wide variety of oscillatory Reynolds and Womersley numbers. An unsteady version of the Johnson–King model was implemented with optional near-wall modification to account for temporal pressure gradient variations, and the predictions were compared with those of the Spalart–Allmaras and k–ε turbulence models. Transition and relaminarization were based on empirical Womersley number correlations and assumed to occur instantaneously: in the former case, this assumption was valid, but in the latter case, deviations between data and predictions were observed. In flows where the oscillatory Reynolds numbers are substantially higher than the commonly accepted steady critical value (~2000), fully or continuously turbulent models produced the best correspondence with experimental data. Critically and conditionally turbulent models produced slightly inferior correspondence, and no significant benefit was observed when near-wall pressure gradient effects were implemented or when common one- and two-equation turbulence models were employed. The turbulent velocity profiles were mainly unaffected by the oscillations and this was explained by noting that the turbulent viscosity is significantly higher than its laminar counterpart. Thus, a turbulent Womersley number was proposed for the analysis and categorization of oscillatory pipe flows. Full article

(This article belongs to the Special Issue Turbulence and Fluid Mechanics)

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27 pages, 60047 KiB

Open AccessArticle

CTF and FLOCAL Thermal Hydraulics Validations and Verifications within a Multiscale and Multiphysics Software Development

by Sebastian Davies, Ulrich Rohde, Dzianis Litskevich, Bruno Merk, Paul Bryce, Andrew Levers, Anna Detkina, Seddon Atkinson and Venkata Ravindra

Energies 2021, 14(5), 1220; https://0-doi-org.brum.beds.ac.uk/10.3390/en14051220 - 24 Feb 2021

Cited by 8 | Viewed by 2456

Abstract

Simulation codes allow one to reduce the high conservativism in nuclear reactor design improving the reliability and sustainability associated with nuclear power. Full-core coupled reactor physics at the rod level are not provided by most simulation codes. This has led in the UK to the development of a multiscale and multiphysics software development focused on LWRS. In terms of the thermal hydraulics, simulation codes suitable for this multiscale and multiphysics software development include the subchannel code CTF and the thermal hydraulics module FLOCAL of the nodal code DYN3D. In this journal article, CTF and FLOCAL thermal hydraulics validations and verifications within the multiscale and multiphysics software development have been performed to evaluate the accuracy and methodology available to obtain thermal hydraulics at the rod level in both simulation codes. These validations and verifications have proved that CTF is a highly accurate subchannel code for thermal hydraulics. In addition, these verifications have proved that CTF provides a wide range of crossflow and turbulent mixing methods, while FLOCAL in general provides the simplified no-crossflow method as the rest of the methods were only tested during its implementation into DYN3D. Full article

(This article belongs to the Special Issue Turbulence and Fluid Mechanics)

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20 pages, 9305 KiB

Open AccessArticle

Collapse of n Point Vortices, Formation of the Vortex Sheets and Transport of Passive Markers

by Henryk Kudela

Energies 2021, 14(4), 943; https://0-doi-org.brum.beds.ac.uk/10.3390/en14040943 - 11 Feb 2021

Cited by 3 | Viewed by 2203

Abstract

In this paper, the motion of the n-vortex system as it collapses to a point in finite time is studied. The motion of vortices is described by the set of ordinary differential equations that we are able to solve analytically. The explicit formula for the solution demands the initial location of collapsing vortices. To find the collapsing locations of vortices, the algebraic, nonlinear system of equations was built. The solution of that algebraic system was obtained using Newton’s procedure. A good initial iterate needs to be provided to succeed in the application of Newton’s procedure. An unconstrained Leverber–Marquart optimization procedure was used to find such a good initial iterate. The numerical studies were conducted, and numerical evidence was presented that if in a collapsing system

n = 50

point vortices include a few vortices with much greater intensities than the others in the set, the vortices with weaker intensities organize themselves onto the vortex sheet. The collapsing locations depend on the value of the Hamiltonian. By changing the Hamiltonian values in a specific interval, the collapsing curves can be obtained. All points on the collapse curves with the same Hamiltonian value represent one collapsing system of vortices. To show the properties of vortex sheets created by vortices, the passive tracers were used. Advection of tracers by the velocity induced by vortices was calculated by solving the proper differential equations. The vortex sheets are an impermeable barrier to inward and outward fluxes of tracers. Arising vortex structures are able to transport the passive tracers. In this paper, several examples showing the diversity of collapsing structures with the vortex sheet are presented. The collapsing phenomenon of many vortices, their ability to self organize and the transportation of the passive tracers are novelties in the context of point vortex dynamics. Full article

(This article belongs to the Special Issue Turbulence and Fluid Mechanics)

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12 pages, 6334 KiB

Open AccessArticle

A Simplified Method for Modeling of Pressure Losses and Heat Transfer in Fixed-Bed Reactors with Low Tube-to-Particle Diameter Ratio

by Tymoteusz Świeboda, Renata Krzyżyńska, Anna Bryszewska-Mazurek, Wojciech Mazurek and Alicja Wysocka

Energies 2021, 14(3), 784; https://0-doi-org.brum.beds.ac.uk/10.3390/en14030784 - 02 Feb 2021

Cited by 2 | Viewed by 1910

Abstract

This manuscript presents a simplified method of modeling fixed-bed reactors based on the porous medium. The proposed method primarily allows the necessity of precisely mapping the internal structure of the bed—which usually is done using real object imaging techniques (like X-ray tomography) or numerical methods (like discrete element method (DEM))—to be avoided. As a result, problems with generating a good quality numerical mesh at the particles’ contact points using special techniques, such as by flattening spheres or the caps method, are also eliminated. The simplified method presented in the manuscript is based on the porous medium method. Preliminary research has shown that the porous medium method needs modifications. This is because of channeling, wall effects, and local backflows, which are substantial factors in reactors with small values of tube-to-particle-diameter ratio. The anisotropic thermal conductivity coefficient was introduced to properly reproduce heat transfer in the direction perpendicular to the general fluid flow. Since the commonly used fixed-bed reactor models validation method based on comparing the velocity and temperature profiles in the selected bed cross-section is not justified in the case of the porous medium method, an alternative method was proposed. The validation method used in this work is based on the mass-weighted average temperature increase and area-weighted average pressure drop between two control cross-section of the reactor. Thanks to the use of the described method, it is possible to obtain satisfactorily accurate results of the fixed-bed reactor model with no cumbersome mesh preparation and long-term calculations. Full article

(This article belongs to the Special Issue Turbulence and Fluid Mechanics)

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25 pages, 7046 KiB

Open AccessArticle

Impact of Chemistry–Turbulence Interaction Modeling Approach on the CFD Simulations of Entrained Flow Coal Gasification

by Jakub Mularski and Norbert Modliński

Energies 2020, 13(23), 6467; https://0-doi-org.brum.beds.ac.uk/10.3390/en13236467 - 07 Dec 2020

Cited by 13 | Viewed by 2486

Abstract

This paper examines the impact of different chemistry–turbulence interaction approaches on the accuracy of simulations of coal gasification in entrained flow reactors. Infinitely fast chemistry is compared with the eddy dissipation concept considering the influence of turbulence on chemical reactions. Additionally, ideal plug flow reactor study and perfectly stirred reactor study are carried out to estimate the accuracy of chosen simplified chemical kinetic schemes in comparison with two detailed mechanisms. The most accurate global approach and the detailed one are further implemented in the computational fluid dynamics (CFD) code. Special attention is paid to the water–gas shift reaction, which is found to have the key impact on the final gas composition. Three different reactors are examined: a pilot-scale Mitsubishi Heavy Industries reactor, a laboratory-scale reactor at Brigham Young University and a Conoco-Philips E-gas reactor. The aim of this research was to assess the impact of gas phase reaction model accuracy on simulations of the entrained flow gasification process. The investigation covers the following issues: impact of the choice of gas phase kinetic reactions mechanism as well as influence of the turbulence–chemistry interaction model. The advanced turbulence–chemistry models with the complex kinetic mechanisms showed the best agreement with the experimental data. Full article

(This article belongs to the Special Issue Turbulence and Fluid Mechanics)

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23 pages, 7497 KiB

Open AccessArticle

Effects of an Inlet Vortex on the Performance of an Axial-Flow Pump

by Wenpeng Zhang, Fangping Tang, Lijian Shi, Qiujin Hu and Ying Zhou

Energies 2020, 13(11), 2854; https://0-doi-org.brum.beds.ac.uk/10.3390/en13112854 - 03 Jun 2020

Cited by 16 | Viewed by 2633

Abstract

The formation of an inlet vortex seriously restricts axial-flow pump device performance and poses a great threat to the safe and stable operation of the entire system. In this study, the change trends of an inlet vortex and its influence on an axial-flow pump are investigated numerically and experimentally in a vertical axial-flow pump device. Four groups of fixed vortex generators (VGs) are installed in front of the impeller to create stable vortices at the impeller inlet. The vortex influence on the performance of pump device is qualitatively and quantitatively analyzed. The vortex patterns at different positions and moments in the pump device are explored to reveal the vortex shape change trend in the impeller and the pressure fluctuation induced by the vortex. The reliability and accuracy of steady and unsteady numerical results are verified by external characteristics and pressure fluctuation experimental results. Results show that it is feasible to install VGs before the impeller inlet to generate stable vortices. The vortex disturbs the inlet flow fields of the impeller, resulting in significant reductions of the axial velocity weighted average angle and the axial velocity uniformity. The vortex increases the inlet passage hydraulic loss and reduces the impeller efficiency, while it only slightly affects the guide vane and outlet passage performance. The vortex causes a low-frequency pressure pulsation and interacts with the impeller. The closer the vortex is to the impeller inlet, the more significant the impeller influence on the vortex. The blade cuts off the vortex in the impeller; afterwards, the vortex follows the blade rotation, and its strength weakens. Full article

(This article belongs to the Special Issue Turbulence and Fluid Mechanics)

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Review

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56 pages, 9940 KiB

Open AccessReview

Hydrodynamics of Liquid-Liquid Flows in Micro Channels and Its Influence on Transport Properties: A Review

by Arijit A. Ganguli and Aniruddha B. Pandit

Energies 2021, 14(19), 6066; https://0-doi-org.brum.beds.ac.uk/10.3390/en14196066 - 23 Sep 2021

Cited by 13 | Viewed by 2670

Abstract

Hydrodynamics plays a major role in transport of heat and mass transfer in microchannels. This includes flow patterns and flow regimes in which the micro-channels are operated. The flow patterns have a major impact the transport properties. Another important aspect is the pressure drop in micro-channels. In the present review, the experimental and Computational Fluid Dynamics (CFD) studies covering all the above aspects have been covered. The effect of geometrical parameters like shape of channel, channel size, material of construction of channels; operating parameters like flow velocity, flow ratio and fluid properties have been presented and analyzed. Experimental and analytical work of different pressure drop models has also been presented. All the literature related to influence of flow patterns on transport properties like volumetric mass transfer coefficients (VMTC) and heat transfer coefficients (HTC) have been presented and analyzed. It is found that most works in Liquid-Liquid Extraction (LLE) systems have been carried out in slug flow and T-junctions. Models for coupled systems of flow and mass transfer have been presented and works carried out for different coupled systems have been listed. CFD simulations match experimental results within 20% deviations in quantitative and qualitative predictions of flow phenomena for most research articles referred in this review. There is a disparity in prediction of a generalized regime map and a generalized regime map for prediction of flow patterns for various systems would need the help of Artificial Intelligence. Full article

(This article belongs to the Special Issue Turbulence and Fluid Mechanics)

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