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Thermal Flows
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Thermal Flows

A special issue of Fluids (ISSN 2311-5521). This special issue belongs to the section "Heat and Mass Transfer".

Deadline for manuscript submissions: closed (15 December 2020) | Viewed by 24877

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editor

Prof. Dr. Marcello Lappa

E-Mail Website
Guest Editor
Department of Mechanical and Aerospace Engineering, University of Strathclyde, James Weir Building, 75 Montrose Street, Glasgow G1 1XJ, UK
Interests: thermogravitational flows; multiphase flows; solid particle dynamics; CFD applied to materials processing; thermocapillary (Marangoni) flows; thermovibrational flows; methods of numerical analysis in computational fluid dynamics and heat/mass transfer; high performance computing; biological fluid dynamics; tissue engineering and CFD

Special Issue Information

Dear Colleagues,

Flows of thermal origin and related heat transfer problems are central in a variety of disciplines and industrial applications. The aim of this Special Issue is to create a collection of studies by distinct investigators and research groups dealing with different types of thermal flows relevant to typical natural or technological contexts (e.g., thermogravitational, thermocapillary and thermovibrational convection).

In particular, we seek manuscripts that present the state-of-the-art and/or a review of the existing knowledge, as well as new theoretical, numerical or experimental investigations on the structure of these flows, their stability behavior and the possible bifurcations to different patterns of symmetry and/or spatiotemporal regimes. Studies concerned with different categories of fluids are welcome (including, but not limited to: liquid metals, molten salts and semiconductors, gases, common fluids such as water, oils, organic and inorganic transparent liquids, molten plastics, polymeric fluids and viscoelastic liquids, etc.). Significant room will also devoted to analyses focused on “hybrid” cases where the considered thermal flow is driven by more than one driving force (mixed convection), it occurs in rotating systems or in the presence of other effects such as forced convection, solidification and/or magnetic fields.

This collection of papers will constitute a new important resource for physicists, engineers, and advanced students interested in the physics of non-isothermal fluid systems, fluid mechanics, environmental phenomena, meteorology, geophysics, thermal and (especially) materials engineering.

Prof. Dr. Marcello Lappa
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. Fluids is an international peer-reviewed open access monthly 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 1800 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

  • buoyancy flow
  • surface-tension driven convention
  • thermovibrational flow
  • rotating fluids
  • Newtonian fluids
  • viscoelastic liquids
  • patterning behaviour
  • instabilities
  • bifurcations
  • transition to chaos
  • linear stability analysis
  • amplitude equations
  • computational fluid dynamics
  • experimental analysis

Published Papers (12 papers)

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Editorial

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3 pages, 168 KiB  
Editorial
Thermal Flows
by Marcello Lappa
Fluids 2021, 6(6), 227; https://0-doi-org.brum.beds.ac.uk/10.3390/fluids6060227 - 18 Jun 2021
Viewed by 1187
Abstract
Flows of thermal origin and heat transfer problems are central in a variety of disciplines and industrial applications [...] Full article
(This article belongs to the Special Issue Thermal Flows)

Research

Jump to: Editorial

12 pages, 2929 KiB  
Article
Vibroconvective Patterns in a Layer under Translational Vibrations of Circular Polarization
by Victor Kozlov, Kirill Rysin and Aleksei Vjatkin
Fluids 2021, 6(3), 108; https://0-doi-org.brum.beds.ac.uk/10.3390/fluids6030108 - 06 Mar 2021
Cited by 4 | Viewed by 1326
Abstract
This article experimentally investigates thermal vibrational convection in horizontal layers, subject to circular translational oscillations in the horizontal plane. The definite direction of translational vibrations lacks investigation, and the case of a layer heated from above is considered. At large negative values of [...] Read more.
This article experimentally investigates thermal vibrational convection in horizontal layers, subject to circular translational oscillations in the horizontal plane. The definite direction of translational vibrations lacks investigation, and the case of a layer heated from above is considered. At large negative values of the gravitational Rayleigh number, the thermovibrational convection appears in a threshold manner with an increase in the vibration intensity. Our results show that in the case of strong gravitational stabilization, thermovibrational convection develops in the form of patterns with strong anisotropy of spatial periods in orthogonal directions. The vibroconvective patterns have the form of parallel rolls divided along their length into relatively short segments. The layer thickness determines the distance between the rolls, and the longitudinal wavelength, depends on the Rayleigh number. Convective cells are studied using the noninvasive thermohromic methodic. It is found that when using the tracers for flow visualization, the concentration and type of the visualizer particles have a serious impact on the shape of the observed vibroconvective structures. In particular, the presence of even a small number of tracers (used in the study of velocity fields by the PIV method) generates flows and intensifies the heat transfer below the threshold of thermovibrational convection excitation. Full article
(This article belongs to the Special Issue Thermal Flows)
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16 pages, 5619 KiB  
Article
Experimental Study on Coherent Structures by Particles Suspended in Half-Zone Thermocapillary Liquid Bridges: Review
by Ichiro Ueno
Fluids 2021, 6(3), 105; https://0-doi-org.brum.beds.ac.uk/10.3390/fluids6030105 - 04 Mar 2021
Cited by 8 | Viewed by 1804
Abstract
Coherent structures by the particles suspended in the half-zone thermocapillary liquid bridges via experimental approaches are introduced. General knowledge on the particle accumulation structures (PAS) is described, and then the spatial–temporal behaviours of the particles forming the PAS are illustrated with the results [...] Read more.
Coherent structures by the particles suspended in the half-zone thermocapillary liquid bridges via experimental approaches are introduced. General knowledge on the particle accumulation structures (PAS) is described, and then the spatial–temporal behaviours of the particles forming the PAS are illustrated with the results of the two- and three-dimensional particle tracking. Variations of the coherent structures as functions of the intensity of the thermocapillary effect and the particle size are introduced by focusing on the PAS of the azimuthal wave number m=3. Correlation between the particle behaviour and the ordered flow structures known as the Kolmogorov–Arnold—Moser tori is discussed. Recent works on the PAS of m=1 are briefly introduced. Full article
(This article belongs to the Special Issue Thermal Flows)
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15 pages, 4818 KiB  
Article
Time-Periodic Cooling of Rayleigh–Bénard Convection
by Lyes Nasseri, Nabil Himrane, Djamel Eddine Ameziani, Abderrahmane Bourada and Rachid Bennacer
Fluids 2021, 6(2), 87; https://0-doi-org.brum.beds.ac.uk/10.3390/fluids6020087 - 16 Feb 2021
Cited by 5 | Viewed by 2219
Abstract
The problem of Rayleigh–Bénard’s natural convection subjected to a temporally periodic cooling condition is solved numerically by the Lattice Boltzmann method with multiple relaxation time (LBM-MRT). The study finds its interest in the field of thermal comfort where current knowledge has gaps in [...] Read more.
The problem of Rayleigh–Bénard’s natural convection subjected to a temporally periodic cooling condition is solved numerically by the Lattice Boltzmann method with multiple relaxation time (LBM-MRT). The study finds its interest in the field of thermal comfort where current knowledge has gaps in the fundamental phenomena requiring their exploration. The Boussinesq approximation is considered in the resolution of the physical problem studied for a Rayleigh number taken in the range 103 ≤ Ra ≤ 106 with a Prandtl number equal to 0.71 (air as working fluid). The physical phenomenon is also controlled by the amplitude of periodic cooling where, for small values of the latter, the results obtained follow a periodic evolution around an average corresponding to the formulation at a constant cold temperature. When the heating amplitude increases, the physical phenomenon is disturbed, the stream functions become mainly multicellular and an aperiodic evolution is obtained for the heat transfer illustrated by the average Nusselt number. Full article
(This article belongs to the Special Issue Thermal Flows)
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13 pages, 944 KiB  
Article
Onset of Inertial Magnetoconvection in Rotating Fluid Spheres
by Radostin D. Simitev and Friedrich H. Busse
Fluids 2021, 6(1), 41; https://0-doi-org.brum.beds.ac.uk/10.3390/fluids6010041 - 13 Jan 2021
Cited by 3 | Viewed by 2291
Abstract
The onset of convection in the form of magneto-inertial waves in a rotating fluid sphere permeated by a constant axial electric current is studied in this paper. Thermo-inertial convection is a distinctive flow regime on the border between rotating thermal convection and wave [...] Read more.
The onset of convection in the form of magneto-inertial waves in a rotating fluid sphere permeated by a constant axial electric current is studied in this paper. Thermo-inertial convection is a distinctive flow regime on the border between rotating thermal convection and wave propagation. It occurs in astrophysical and geophysical contexts where self-sustained or external magnetic fields are commonly present. To investigate the onset of motion, a perturbation method is used here with an inviscid balance in the leading order and a buoyancy force acting against weak viscous dissipation in the next order of approximation. Analytical evaluation of constituent integral quantities is enabled by applying a Green’s function method for the exact solution of the heat equation following our earlier non-magnetic analysis. Results for the case of thermally infinitely conducting boundaries and for the case of nearly thermally insulating boundaries are obtained. In both cases, explicit expressions for the dependence of the Rayleigh number on the azimuthal wavenumber are derived in the limit of high thermal diffusivity. It is found that an imposed azimuthal magnetic field exerts a stabilizing influence on the onset of inertial convection and as a consequence magneto-inertial convection with azimuthal wave number of unity is generally preferred. Full article
(This article belongs to the Special Issue Thermal Flows)
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18 pages, 7414 KiB  
Article
Non-Modal Three-Dimensional Optimal Perturbation Growth in Thermally Stratified Mixing Layers
by Helena Vitoshkin and Alexander Gelfgat
Fluids 2021, 6(1), 37; https://0-doi-org.brum.beds.ac.uk/10.3390/fluids6010037 - 11 Jan 2021
Cited by 3 | Viewed by 1963
Abstract
A non-modal transient disturbances growth in a stably stratified mixing layer flow is studied numerically. The model accounts for a density gradient within a shear region, implying a heavier layer at the bottom. Numerical analysis of non-modal stability is followed by a full [...] Read more.
A non-modal transient disturbances growth in a stably stratified mixing layer flow is studied numerically. The model accounts for a density gradient within a shear region, implying a heavier layer at the bottom. Numerical analysis of non-modal stability is followed by a full three-dimensional direct numerical simulation (DNS) with the optimally perturbed base flow. It is found that the transient growth of two-dimensional disturbances diminishes with the strengthening of stratification, while three-dimensional disturbances cause significant non-modal growth, even for a strong, stable stratification. This non-modal growth is governed mainly by the Holmboe modes and does not necessarily weaken with the increase of the Richardson number. The optimal perturbation consists of two waves traveling in opposite directions. Compared to the two-dimensional transient growth, the three-dimensional growth is found to be larger, taking place at shorter times. The non-modal growth is observed in linearly stable regimes and, in slightly linearly supercritical regimes, is steeper than that defined by the most unstable eigenmode. The DNS analysis confirms the presence of the structures determined by the transient growth analysis. Full article
(This article belongs to the Special Issue Thermal Flows)
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23 pages, 14025 KiB  
Article
The Zoo of Modes of Convection in Liquids Vibrated along the Direction of the Temperature Gradient
by Georgie Crewdson and Marcello Lappa
Fluids 2021, 6(1), 30; https://0-doi-org.brum.beds.ac.uk/10.3390/fluids6010030 - 08 Jan 2021
Cited by 15 | Viewed by 2302
Abstract
Thermovibrational flow can be seen as a variant of standard thermogravitational convection where steady gravity is replaced by a time-periodic acceleration. As in the parent phenomena, this type of thermal flow is extremely sensitive to the relative directions of the acceleration and the [...] Read more.
Thermovibrational flow can be seen as a variant of standard thermogravitational convection where steady gravity is replaced by a time-periodic acceleration. As in the parent phenomena, this type of thermal flow is extremely sensitive to the relative directions of the acceleration and the prevailing temperature gradient. Starting from the realization that the overwhelming majority of research has focused on circumstances where the directions of vibrations and of the imposed temperature difference are perpendicular, we concentrate on the companion case in which they are parallel. The increased complexity of this situation essentially stems from the properties that are inherited from the corresponding case with steady gravity, i.e., the standard Rayleigh–Bénard convection. The need to overcome a threshold to induce convection from an initial quiescent state, together with the opposite tendency of acceleration to damp fluid motion when its sign is reversed, causes a variety of possible solutions that can display synchronous, non-synchronous, time-periodic, and multi-frequency responses. Assuming a square cavity as a reference case and a fluid with Pr = 15, we tackle the problem in a numerical framework based on the solution of the governing time-dependent and non-linear equations considering different amplitudes and frequencies of the applied vibrations. The corresponding vibrational Rayleigh number spans the interval from Raω = 104 to Raω = 106. It is shown that a kaleidoscope of possible variants exist whose nature and variety calls for the simultaneous analysis of their temporal and spatial behavior, thermofluid-dynamic (TFD) distortions, and the Nusselt number, in synergy with existing theories on the effect of periodic accelerations on fluid systems. Full article
(This article belongs to the Special Issue Thermal Flows)
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11 pages, 290 KiB  
Article
Determination of Critical Reynolds Number for the Flow Near a Rotating Disk on the Basis of the Theory of Stochastic Equations and Equivalence of Measures
by Artur V. Dmitrenko
Fluids 2021, 6(1), 5; https://0-doi-org.brum.beds.ac.uk/10.3390/fluids6010005 - 25 Dec 2020
Cited by 8 | Viewed by 2087
Abstract
The determination of the flow regime of liquid and gas in power plants is the most important design task. Performing the calculations based on modern calculation methods requires a priori knowledge of the initial and boundary conditions, which significantly affect the final results. [...] Read more.
The determination of the flow regime of liquid and gas in power plants is the most important design task. Performing the calculations based on modern calculation methods requires a priori knowledge of the initial and boundary conditions, which significantly affect the final results. The purpose of the article is to present the solution for the critical Reynolds number for the flow near a rotating disk on the basis of the theory of stochastic equations of continuum laws and equivalence of measures between random and deterministic motions. The determination of the analytical dependence for the critical Reynolds number is essential for the study of flow regimes and the thermal state of disks and blades in the design of gas and steam turbines. The result of the calculation with using the new formula shows that for the flow near a wall of rotating disk, the critical Reynolds number is 325,000, when the turbulent Reynolds is 5 ÷ 10 and the degree of turbulence is 0.01 ÷ 0.02. Therefore, the result of solution shows a satisfactory correspondence of the obtained analytical dependence for the critical Reynolds number with the experimental data. Full article
(This article belongs to the Special Issue Thermal Flows)
20 pages, 5989 KiB  
Article
Effects of Shell Thickness on Cross-Helicity Generation in Convection-Driven Spherical Dynamos
by Luis Silva, Parag Gupta, David MacTaggart and Radostin D. Simitev
Fluids 2020, 5(4), 245; https://0-doi-org.brum.beds.ac.uk/10.3390/fluids5040245 - 16 Dec 2020
Cited by 2 | Viewed by 2400
Abstract
The relative importance of the helicity and cross-helicity electromotive dynamo effects for self-sustained magnetic field generation by chaotic thermal convection in rotating spherical shells is investigated as a function of shell thickness. Two distinct branches of dynamo solutions are found to coexist in [...] Read more.
The relative importance of the helicity and cross-helicity electromotive dynamo effects for self-sustained magnetic field generation by chaotic thermal convection in rotating spherical shells is investigated as a function of shell thickness. Two distinct branches of dynamo solutions are found to coexist in direct numerical simulations for shell aspect ratios between 0.25 and 0.6—a mean-field dipolar regime and a fluctuating dipolar regime. The properties characterising the coexisting dynamo attractors are compared and contrasted, including differences in temporal behaviour and spatial structures of both magnetic fields and rotating thermal convection. The helicity α-effect and the cross-helicity γ-effect are found to be comparable in intensity within the fluctuating dipolar dynamo regime, where their ratio does not vary significantly with the shell thickness. In contrast, within the mean-field dipolar dynamo regime the helicity α-effect dominates by approximately two orders of magnitude and becomes stronger with decreasing shell thickness. Full article
(This article belongs to the Special Issue Thermal Flows)
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16 pages, 3577 KiB  
Article
Thermal Performance of a Heated Pipe in the Presence of a Metal Foam and Twisted Tape Inserts
by K. Papazian, Z. Al Hajaj and M. Z. Saghir
Fluids 2020, 5(4), 195; https://0-doi-org.brum.beds.ac.uk/10.3390/fluids5040195 - 30 Oct 2020
Cited by 9 | Viewed by 2185
Abstract
To meet the demand for more efficient ways of cooling and heating, new designs and further development of heat exchangers is essential in industry. The present study focuses on the thermal performance of a circular pipe with two inserts. The first insert consists [...] Read more.
To meet the demand for more efficient ways of cooling and heating, new designs and further development of heat exchangers is essential in industry. The present study focuses on the thermal performance of a circular pipe with two inserts. The first insert consists of a porous medium having a porosity of 0.91, and the second one consists of a single twist solid insert. Different ranges of heating conditions have been applied for different flow rates. Water and titanium dioxide (TiO2) nanofluid 1% vol are the liquid media used for cooling. Laminar flow is assumed for two different Reynolds numbers of 1000 and 2000. The results of the study have shown that the twisted tape insert increases the thermal efficiency of the pipe more than the porous media insert and the plain pipe. In addition, different temperature readings in the cross section of the pipe have indicated that the twisted tape helps mixing up the fluid and provides a constant temperature in the overall volume of the fluid, whereas for the porous media insert and plain pipe the fluid temperature increases in the fluid particles close to the pipe inner surface. TiO2 nanofluid exhibited an enhancement when compared to water for a plain and porous pipe. However, this enhancement was absent when a twisted insert is used. Full article
(This article belongs to the Special Issue Thermal Flows)
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26 pages, 23278 KiB  
Article
Numerical Study of Rotating Thermal Convection on a Hemisphere
by Patrick Fischer, Charles-Henri Bruneau and Hamid Kellay
Fluids 2020, 5(4), 185; https://0-doi-org.brum.beds.ac.uk/10.3390/fluids5040185 - 20 Oct 2020
Cited by 2 | Viewed by 1867
Abstract
Numerical simulations of rotating two-dimensional turbulent thermal convection on a hemisphere are presented in this paper. Previous experiments on a half soap bubble located on a heated plate have been used for studying thermal convection as well as the effects of rotation on [...] Read more.
Numerical simulations of rotating two-dimensional turbulent thermal convection on a hemisphere are presented in this paper. Previous experiments on a half soap bubble located on a heated plate have been used for studying thermal convection as well as the effects of rotation on a curved surface. Here, two different methods have been used to produce the rotation of the hemisphere: the classical rotation term added to the velocity equation, and a non-zero azimuthal velocity boundary condition. This latter method is more adapted to the soap bubble experiments. These two methods of forcing the rotation of the hemisphere induce different fluid dynamics. While the first method is classically used for describing rotating Rayleigh–Bénard convection experiments, the second method seems to be more adapted for describing rotating flows where a shear layer may be dominant. This is particularly the case where the fluid is not contained in a closed container and the rotation is imposed on only one side of it. Four different diagnostics have been used to compare the two methods: the Nusselt number, the effective computation of the convective heat flux, the velocity and temperature fluctuations root mean square (RMS) generation of vertically aligned vortex tubes (to evaluate the boundary layers) and the energy/enstrophy/temperature spectra/fluxes. We observe that the dynamics of the convective heat flux is strongly inhibited by high rotations for the two different forcing methods. Also, and contrary to classical three-dimensional rotating Rayleigh–Bénard convection experiments, almost no significant improvement of the convective heat flux has been observed when adding a rotation term in the velocity equation. However, moderate rotations induced by non-zero velocity boundary conditions induce a significant enhancement of the convective heat flux. This enhancement is closely related to the presence of a shear layer and to the thermal boundary layer just above the equator. Full article
(This article belongs to the Special Issue Thermal Flows)
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51 pages, 3435 KiB  
Article
Coating Flow Near Channel Exit. A Theoretical Perspective
by Roger E. Khayat and Mohammad Tanvir Hossain
Fluids 2020, 5(4), 180; https://0-doi-org.brum.beds.ac.uk/10.3390/fluids5040180 - 15 Oct 2020
Cited by 1 | Viewed by 2214
Abstract
The planar flow of a steady moving-wall free-surface jet is examined theoretically for moderate inertia and surface tension. The method of matched asymptotic expansion and singular perturbation is used to explore the rich dynamics near the stress singularity. A thin-film approach is also [...] Read more.
The planar flow of a steady moving-wall free-surface jet is examined theoretically for moderate inertia and surface tension. The method of matched asymptotic expansion and singular perturbation is used to explore the rich dynamics near the stress singularity. A thin-film approach is also proposed to capture the flow further downstream where the flow becomes of the boundary-layer type. We exploit the similarity character of the flow to circumvent the presence of the singularity. The study is of close relevance to slot and blade coating. The jet is found to always contract near the channel exit, but presents a mild expansion further downstream for a thick coating film. We predict that separation occurs upstream of the exit for slot coating, essentially for any coating thickness near the moving substrate, and for a thin film near the die. For capillary number of order one, the jet profile is not affected by surface tension but the normal stress along the free surface exhibits a maximum that strengthens with surface tension. In contrast to existing numerical findings, we predict the existence of upstream influence as indicated by the nonlinear pressure dependence on upstream distance and the pressure undershoot (overshoot) in blade (slot) coating at the exit. Full article
(This article belongs to the Special Issue Thermal Flows)
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