Physics in Engineering: A Themed Issue in Honour of Professor Peter Vadasz on the Occasion of His 70th Birthday

A special issue of Physics (ISSN 2624-8174). This special issue belongs to the section "Classical Physics".

Deadline for manuscript submissions: closed (28 February 2022) | Viewed by 18324

Special Issue Editors


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Guest Editor
Department of Mechanical Engineering, University of Bath, Bath BA2 7AY, UK
Interests: convection; porous media; instability; numerical simulation; asymptotic analysis; non-Newtonian fluids
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Guest Editor
1. Eskom Holdings SOC, Maxwell Drive, Sunninghill, Sandton, PO Box 1091 Johannesburg, South Africa
2. School of Mechanical Engineering, University of Kwa Zulu Natal, Durban 4000, South Africa

Special Issue Information

Dear Colleagues,

text

It is our priviledge and honour to guest edit this Special Issue, which is dedicated to Professor Peter Vadasz on the occasion of his 70th birthday. Although he has many interests, he is an eminent leader and authority on the study of convective instabilities in porous media and has a particular interest in rotating systems of different kinds. He has dedicated much of his career to such systems and has recently published the well-received monograph, “Fluid Flow and Heat Transfer in Rotating Porous Media”. He has also been honoured by having the Vadasz number named for him.

Besides being an exemplary scientist he was/is known for having the “Vadasz Effect” as a teacher. He joined the University of Durban-Westville in 1991 at a crucial time in the engineering faculty’s history. As a start, he led a team that resulted in the engineering faculty receiving full accreditation from the Engineering Council of South Africa (ECSA). From that point on, his academic and administrative prowess became legendary. His students have described him as someone who is down to earth and approachable, to the extent that his lectures were always filled with interesting content, international affairs and very interesting scientific titbits that you could never read about. A student can attest to this. His inspiration, openness, and willingness to share his knowledge has inspired hundreds of students that graduated under him. To that end, most of those students try to mimic his work ethic and principles and today hold important and influential positions in key institutes/organizations. In 2002, Professor Peter Vadasz joined Northern Arizona University as the chair of mechanical engineering, where he is currently employed today. 

Dr. D. Andrew Rees
Dr. Saneshan Govender
Guest Editors

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Keywords

  • instability
  • convection
  • rotating systems
  • weak turbulence
  • nanofluids
  • transport phenomena in porous media
  • fluid dynamics
  • heat transfer
  • nanotechnology–nano-heat transfer
  • biological engineering
  • investigation of nonlinear effects-stability, bifurcation, and routes to chaos
  • physical and mathematical modeling and simulations

Published Papers (9 papers)

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Research

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15 pages, 2833 KiB  
Article
Free Convection of a Bingham Fluid in a Differentially-Heated Porous Cavity: The Effect of a Square Grid Microstructure
by D. Andrew S. Rees
Physics 2022, 4(1), 202-216; https://doi.org/10.3390/physics4010015 - 10 Feb 2022
Cited by 2 | Viewed by 1779
Abstract
We examine how a square-grid microstructure affects the manner in which a Bingham fluid is convected in a sidewall-heated rectangular porous cavity. When the porous microstructure is isotropic, flow arises only when the Darcy–Rayleigh number is higher than a critical value, and this [...] Read more.
We examine how a square-grid microstructure affects the manner in which a Bingham fluid is convected in a sidewall-heated rectangular porous cavity. When the porous microstructure is isotropic, flow arises only when the Darcy–Rayleigh number is higher than a critical value, and this corresponds to when buoyancy forces are sufficient to overcome the yield threshold of the Bingham fluid. In such cases, the flow domain consists of a flowing region and stagnant regions within which there is no flow. Here, we consider a special case where the constituent pores form a square grid pattern. First, we use a network model to write down the appropriate macroscopic momentum equations as a Darcy–Bingham law for this microstructure. Then detailed computations are used to determine strongly nonlinear states. It is found that the flow splits naturally into four different regions: (i) full flow, (ii) no-flow, (iii) flow solely in the horizontal direction and (iv) flow solely in the vertical direction. The variations in the rate of heat transfer and the strength of the flow with the three governing parameters, the Darcy–Rayleigh number, Ra, the Rees–Bingham number, Rb, and the aspect ratio, A, are obtained. Full article
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15 pages, 2538 KiB  
Article
The Influence of Bounding Plates on Species Separation in a Vertical Thermogravitational Column
by Abdelkader Mojtabi, Pierre Costeseque, Bafétigué Ouattara, Marie-Catherine Charrier-Mojtabi and D. Andrew S. Rees
Physics 2022, 4(1), 51-65; https://doi.org/10.3390/physics4010005 - 18 Jan 2022
Viewed by 2078
Abstract
In this paper, an analytical and numerical analysis of the species separation in a binary mixture is performed. The main objective is to study the influence of the thickness and the nature of the bounding plates of the thermogravitational column (TGC) on species [...] Read more.
In this paper, an analytical and numerical analysis of the species separation in a binary mixture is performed. The main objective is to study the influence of the thickness and the nature of the bounding plates of the thermogravitational column (TGC) on species separation. The theory of Furry, Jones and Onsager is extended to the cases where bounding conducting walls enclose the TGC. The governing 2-dimensional equations are solved numerically using COMSOL Multiphysics software. A good agreement is found between the analytical and the numerical results. It is shown that the determination of the thermal diffusion coefficient, DT, from the measurement of the vertical mass fraction gradient of binary solutions, does not depend on the temperature difference imposed on the vertical column either on the outer walls of the cavity or on the inner walls in contact with the binary solutions. However, it is found that this result is no longer valid in the case of a binary gas. To our knowledge, in all earlier studies, dealing with the measurement of Soret coefficients in binary fluids, the nature and the thickness of the bounding walls were not considered. Full article
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14 pages, 30990 KiB  
Article
Magnetic Resonance Velocimetry Measurement of Viscous Flows through Porous Media: Comparison with Simulation and Voxel Size Study
by Martin Bruschewski, Sam Flint and Sid Becker
Physics 2021, 3(4), 1254-1267; https://doi.org/10.3390/physics3040079 - 20 Dec 2021
Cited by 2 | Viewed by 2645
Abstract
Studies that use magnetic resonance velocimetry (MRV) to assess flows through porous media require a sufficiently small voxel size to determine the velocity field at a sub-pore scale. The smaller the voxel size, the less information is lost through the discretization. However, the [...] Read more.
Studies that use magnetic resonance velocimetry (MRV) to assess flows through porous media require a sufficiently small voxel size to determine the velocity field at a sub-pore scale. The smaller the voxel size, the less information is lost through the discretization. However, the measurement uncertainty and the measurement time are increased. Knowing the relationship between voxel size and measurement accuracy would help researchers select a voxel size that is not too small in order to avoid unnecessary measurement effort. This study presents a systematic parameter study with a low-Reynolds-number flow of a glycerol–water mixture sent through a regularly periodic porous matrix with a pore size of 5 mm. The matrix was a 3-dimensional polymer print, and velocity-encoded MRV measurements were made at 15 different voxel sizes between 0.42 mm and 4.48 mm. The baseline accuracy of the MRV velocity data was examined through a comparison with a computational fluid dynamics (CFD) simulation. The experiment and simulation show very good agreement, indicating a low measurement error. Starting from the smallest examined voxel size, the influence of the voxel size on the accuracy of the velocity data was then examined. This experiment enables us to conclude that a voxel size of 0.96 mm, which corresponds to 20% of the pore size, is sufficient. The volume-averaged results do not change below a voxel size of 20% of the pore size, whereas systematic deviations occur with larger voxels. The same trend is observed with the local velocity data. The streamlines calculated from the MRV velocity data are not influenced by the voxel size for voxels of up to 20% of the pore size, and even slightly larger voxels still show good agreement. In summary, this study shows that even with a relatively low measurement resolution, quantitative 3-dimensional velocity fields can be obtained through porous flow systems with short measurement times and low measurement uncertainty. Full article
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8 pages, 267 KiB  
Article
Instability of Vertical Throughflows in Bidisperse Porous Media
by Florinda Capone and Roberta De Luca
Physics 2021, 3(4), 821-828; https://doi.org/10.3390/physics3040052 - 23 Sep 2021
Cited by 4 | Viewed by 1425
Abstract
In this paper, the instability of a vertical fluid motion, or throughflow, is investigated in a horizontal bidisperse porous layer that is uniformly heated from below. By means of the order-1 Galerkin approximation method, the critical Darcy–Rayleigh number for the onset of steady [...] Read more.
In this paper, the instability of a vertical fluid motion, or throughflow, is investigated in a horizontal bidisperse porous layer that is uniformly heated from below. By means of the order-1 Galerkin approximation method, the critical Darcy–Rayleigh number for the onset of steady instability is determined in closed form. The coincidence between the linear instability threshold and the global nonlinear stability threshold, in the energy norm, is shown. Full article
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11 pages, 1235 KiB  
Article
Vadasz Number Effects on Convection in a Vertical Rotating Porous Layer, Placed Far from Axis of Rotation, and Subjected to Internal Heat Generation and Centrifugal Jitter
by Saneshan Govender
Physics 2021, 3(3), 728-738; https://doi.org/10.3390/physics3030044 - 01 Sep 2021
Viewed by 1683
Abstract
The flow and heat transfer in a rotating vertical porous layer, placed far from the axis of rotation, and subjected to internal heat generation and centrifugal jitter, is considered. The linear stability theory is used to determine the convection threshold, in terms of [...] Read more.
The flow and heat transfer in a rotating vertical porous layer, placed far from the axis of rotation, and subjected to internal heat generation and centrifugal jitter, is considered. The linear stability theory is used to determine the convection threshold, in terms of the critical Rayleigh number. Typical liquids used in engineering applications and heavy liquid metals are used to demonstrate conditions at which the Vadasz number is sufficiently small to warrant the retention of the time derivative in the momentum equation. When considering low amplitude and high frequency approximation, the results show that vibration has a stabilizing effect on the onset of convection. The impact of increasing the Vadasz number is to stabilize the convection, in addition to reducing the transition point from synchronous to subharmonic solutions. In summary, when the Vadasz number is large, centrifugal jitter has no impact on the convection stability criteria. In contrast, when the Vadasz number is small, centrifugal jitter impacts the convection stability criteria. Full article
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14 pages, 556 KiB  
Article
Spatially Developing Modes: The Darcy–Bénard Problem Revisited
by Antonio Barletta
Physics 2021, 3(3), 549-562; https://doi.org/10.3390/physics3030034 - 30 Jul 2021
Cited by 9 | Viewed by 1760
Abstract
In this paper, the instability resulting from small perturbations of the Darcy–Bénard system is explored. An analysis based on time–periodic and spatially developing Fourier modes is adopted. The system under examination is a horizontal porous layer saturated by a fluid. The two impermeable [...] Read more.
In this paper, the instability resulting from small perturbations of the Darcy–Bénard system is explored. An analysis based on time–periodic and spatially developing Fourier modes is adopted. The system under examination is a horizontal porous layer saturated by a fluid. The two impermeable and isothermal plane boundaries are considered to have different temperatures, so that the porous layer is heated from below. The spatial instability for the system is defined by taking into account both the spatial growth rate of the perturbation modes and their propagation direction. A comparison with the neutral stability condition determined by using the classical spatially periodic and time–evolving Fourier modes is performed. Finally, the physical meaning of the concept of spatial instability is discussed. In contrast to the classical analysis, based on spatially periodic modes, the spatial instability analysis, involving time–periodic Fourier modes, is found to lead to the conclusion that instability occurs whenever the Rayleigh number is positive. Full article
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14 pages, 2794 KiB  
Article
Considerate Regulation of Output Disturbances
by Eduard Eitelberg
Physics 2021, 3(2), 173-186; https://doi.org/10.3390/physics3020014 - 02 Apr 2021
Viewed by 1708
Abstract
Recently, I have considered a multi-variable feedforward control practice in a novel way being called “considerate control”. It was shown how the considerate control is related to Bristol gains, which indicate accurately either the required increase in input scope or the reduced output [...] Read more.
Recently, I have considered a multi-variable feedforward control practice in a novel way being called “considerate control”. It was shown how the considerate control is related to Bristol gains, which indicate accurately either the required increase in input scope or the reduced output scope as compared to inconsiderate control. Here, considerate control is expanded to regulating control, necessitating some feedback design. Clearly, high-gain feedback leads to considerate control results in low frequency. Considerate pre-compensation decouples loops also at higher frequencies. However, as an analysis of the included examples demonstrates, such considerate design may insert non-minimum phase-lag into loops that did not have it, thus, reducing the loop bandwidth relative to that achievable in a skillful inconsiderate design, sometimes very significantly. As is often the case, there is a trade-off between consideration and performance. Full article
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16 pages, 2522 KiB  
Article
A Hidden Anomaly in the Binary Mixture Natural Convection Subject to Flux Boundary Conditions
by Peter Vadasz
Physics 2021, 3(1), 144-159; https://doi.org/10.3390/physics3010012 - 23 Mar 2021
Cited by 2 | Viewed by 2032
Abstract
The problem of natural convection in a binary mixture subject to realistic boundary conditions of imposed zero mass flux on the solid walls shows solutions that might lead to unrealistic negative values of the mass fraction (or solute concentration). This anomaly is being [...] Read more.
The problem of natural convection in a binary mixture subject to realistic boundary conditions of imposed zero mass flux on the solid walls shows solutions that might lead to unrealistic negative values of the mass fraction (or solute concentration). This anomaly is being investigated in this paper, and a possible way of addressing it is suggested via a mass-fraction-dependent thermodiffusion coefficient that can have negative values in regions of low mass fractions. Full article
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Review

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8 pages, 261 KiB  
Review
Modeling Turbulence in Permeable Media: The Double-Decomposition Concept Revisited
by Marcelo J. S. de Lemos
Physics 2022, 4(1), 124-131; https://doi.org/10.3390/physics4010010 - 27 Jan 2022
Cited by 2 | Viewed by 1866
Abstract
In this article, a concept named double decomposition, which is used to model turbulent flows in porous media, is examined. This concept is based on the idea that in a turbulent flow through a porous matrix, local instantaneous variables can be averaged in [...] Read more.
In this article, a concept named double decomposition, which is used to model turbulent flows in porous media, is examined. This concept is based on the idea that in a turbulent flow through a porous matrix, local instantaneous variables can be averaged in time and space, simultaneously. Depending on how these operators are applied, averaged equations take different forms. In this article, instantaneous local equations are averaged using both operators and a different set of equations resulting from such operations are commented upon. Additional terms proposed for the averaged equations are discussed. Full article
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