Characteristics of high Rayleigh number two-dimensional convection in an open-top porous layer heated from below

1999 ◽  
Vol 394 ◽  
pp. 241-260 ◽  
Author(s):  
ABDELLAH S. M. CHERKAOUI ◽  
WILLIAM S. D. WILCOCK
Keyword(s):  
Rayleigh Number ◽  
Control Volume ◽  
Flow Patterns ◽  
Convective System ◽  
Two Dimensional ◽  
Simpler Algorithm ◽  
Convective Pattern ◽  
Volume Method ◽  
Rayleigh Numbers ◽  
Type Of Transition

Using a control-volume method and the simpler algorithm, we computed steady-state and time-dependent solutions for two-dimensional convection in an open-top porous box, up to a Rayleigh number of 1100. The evolution of the convective system from onset to high Rayleigh numbers is characterized by two types of transitions in the flow patterns. The first type is a decrease in the horizontal aspect ratio of the cells. We observe two such bifurcations. The first occurs at Ra = 107.8 when the convective pattern switches from a steady one-cell roll to a steady two-cell roll. The second occurs at Ra ≈ 510 when an unsteady two-cell roll evolves to a steady four-cell roll. The second type of transition is from a steady to an unsteady pattern and we also observe two of these bifurcations. The first occurs at Ra ≈ 425 in the two-cell convective pattern; the second at Ra ≈ 970 in the four-cell pattern. Both types of bifurcations are associated with an increase in the average vertical convective heat transport. In the bi-cellular solutions, the appearance of non-periodic unsteady convection corresponds to the onset of the expected theoretical scaling Nu ∝ Ra and also to the onset of plume formation. Although our highest quadri-cellular solutions show signs of non-periodic convection, they do not reach the onset of plume formation. An important hysterisis loop exists for Rayleigh numbers in the range 425–505. Unsteady convection appears only in the direction of increasing Rayleigh numbers. In the decreasing direction, steady quadri-cellular flow patterns prevail.

scholarly journals Numerical study of the coupled natural convection with surface radiation in a cylindrical annular enclosure

2020 ◽  
Vol 330 ◽  
pp. 01029
Author(s):  
Mohamed Amine MEDEBBER ◽  
Abderrahmane AISSA ◽  
Belkacem OULD SAID ◽  
Noureddine RETIEL ◽  
Mohammed EL GANAOUI
Keyword(s):  
Natural Convection ◽  
Numerical Study ◽  
Control Volume ◽  
Surface Radiation ◽  
Navier Stokes ◽  
Simpler Algorithm ◽  
Energy Equations ◽  
Volume Method ◽  
Rayleigh Numbers ◽  
Total Average

The interaction of natural convection with thermal radiation of black surfaces in a cylindrical enclosure filled with air has been numerically investigated. The steady-state continuity, Navier-Stokes and energy equations were discretized using the control volume method and solved numerically via the SIMPLER algorithm. Effects of Rayleigh number (Ra), wall emissivity (εp) and height ratio parameter (X) are studied. The result shows that surface radiation significantly altered the temperature distribution and the flow patterns, especially at higher Rayleigh numbers. The total average Nusselt number has also been discussed for valuating heat transfer through the enclosure.

scholarly journals Pressure-Velocity Coupling Schemes for Bouyancy Driven Flow in a Differentially Heated Cavity Using F.V.M and Matlab

2021 ◽  
pp. 19-39
Author(s):  
Purity Mberia ◽  
Stephen Karanja ◽  
Mark Kimathi
Keyword(s):  
Fluid Flow ◽  
Rayleigh Number ◽  
Bench Mark ◽  
Three Dimension ◽  
Two Dimensional ◽  
Central Difference ◽  
Square Enclosure ◽  
Simpler Algorithm ◽  
Simplec Algorithm ◽  
Rayleigh Numbers

Numerical analysis of fluid flow is anchored on the laws of conservation. A challenge in solving the momentum equation arises due to the unavailability of an explicit pressure equation. To avoid solving the pressure term most researchers have eliminated it by cross differentiating the x and the y two dimensional momentum equations and subtracting them. This method introduces more variables to be solved in comparison to the primitive variables and is  restricted to two-dimensional flows as streamlines do not exist in three-dimension. This method thus presents a serious limitation in analysis of fluid flow. In this study an equation for computing pressure has been developed using pressure - velocity coupling and used in solving the governing equations. The performance of three pressure velocity schemes namely; the Semi Implicit Method for Pressure linked Equation (SIMPLE), SIMPLE Revised (SIMPLER) and SIMPLE Consistent (SIMPLEC) for laminar buoyancy driven flow has been tested in order to establish the scheme that gives results consistent with bench mark data. The equations governing the flow are solved iteratively using finite volume method together with the central difference interpolating scheme. The solutions are presented for Rayleigh numbers of 103, 104, and 105. This resulted in the velocity profiles for the SIMPLE, SIMPLER, and SIMPLEC algorithm for a Rayleigh number of 104 and 105 converging to the same path. At a Rayleigh number of 103 however, SIMPLER algorithm undergoes a degradation in convergence with grid refinement at the baffle region. Results predicted by using the SIMPLEC algorithm are thus able to effectively compute the velocity of fluid flow in a differentially heated square enclosure with baffles for both low and higher Rayleigh numbers irrespective of the grid size.

scholarly journals Effect of Rayleigh Number on Internal Eccentricity in a Heated Horizontal Elliptical Cylinder to its Coaxial Square Enclosure

2020 ◽  
Vol 25 (3) ◽  
pp. 17-29
Author(s):  
Abdelkrim Bouras ◽  
Djedid Taloub ◽  
Zied Driss
Keyword(s):  
Heat Transfer ◽  
Rayleigh Number ◽  
Outer Cylinder ◽  
Boussinesq Approximation ◽  
Square Enclosure ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Commercial Code ◽  
Volume Method ◽  
Rayleigh Numbers

AbstractThis paper deals with numerical investigation of a natural convective flow in a horizontal annular space between a heated square inner cylinder and a cold elliptical outer cylinder with a Newtonian fluid. Uniform temperatures are imposed along walls of the enclosure. The governing equations of the problem were solved numerically by the commercial code Fluent, based on the finite volume method and the Boussinesq approximation. The effects of Geometry Ratio GR and Rayleigh numbers on fluid flow and heat transfer performance are investigated. The Rayleigh number is varied from 103 to 106. Throughout the study the relevant results are presented in terms of isotherms, and streamlines. From the results, we found that the increase in the Geometry Ratio B leads to an increase of the heat transfer coefficient. The heat transfer rate in the annulus is translated in terms of the average Nusselt numbers along the enclosure’s sides. Tecplot 7 program was used to plot the curves which cleared these relations and isotherms and streamlines which illustrate the behavior of air through the channel and its variation with other parameters. The results for the streamlines, isotherms, local and average Nusselt numbers average Nusselt numbers are compared with previous works and show good agreement.

The effect of distant side-walls on the evolution and stability of finite-amplitude Rayleigh-Bénard convection

1981 ◽  
Vol 378 (1775) ◽  
pp. 539-566 ◽  
Keyword(s):  
Rayleigh Number ◽  
Prandtl Number ◽  
Finite Amplitude ◽  
Two Dimensional ◽  
Bénard Convection ◽  
Benard Convection ◽  
Side Walls ◽  
Rayleigh Benard Convection ◽  
Rayleigh Numbers ◽  
Rayleigh Benard

A recent study by Cross et al . (1980) has described a class of finite-amplitude phase-winding solutions of the problem of two-dimensional Rayleigh-Bénard convection in a shallow fluid layer of aspect ratio 2 L (≫ 1) confined laterally by rigid side-walls. These solutions arise at Rayleigh numbers R = R 0 + O ( L -1 ) where R 0 is the critical Rayleigh number for the corresponding infinite layer. Nonlinear solutions of constant phase exist for Rayleigh numbers R = R 0 + O ( L -2 ) but of these only the two that bifurcate at the lowest value of R are stable to two-dimensional linearized disturbances in this range (Daniels 1978). In the present paper one set of the class of phase-winding solutions is found to be stable to two-dimensional disturbances. For certain values of the Prandtl number of the fluid and for stress-free horizontal boundaries the results predict that to preserve stability there must be a continual readjustment of the roll pattern as the Rayleigh number is raised, with a corresponding increase in wavelength proportional to R - R 0 . These solutions also exhibit hysteresis as the Rayleigh number is raised and lowered. For other values of the Prandtl number the number of rolls remains unchanged as the Rayleigh number is raised, and the wavelength remains close to its critical value. It is proposed that the complete evolution of the flow pattern from a static state must take place on a number of different time scales of which t = O(( R - R 0 ) -1 ) and t = O(( R - R 0 ) -2 ) are the most significant. When t = O(( R - R 0 ) -1 ) the amplitude of convection rises from zero to its steady-state value, but the final lateral positioning of the rolls is only completed on the much longer time scale t = O(( R - R 0 ) -2 ).

scholarly journals Transient Numerical Analysis of Free Convection in Cylindrical Enclosure

2020 ◽  
Vol 307 ◽  
pp. 01029
Author(s):  
Mohamed Amine Medebber ◽  
Nourddine Retiel ◽  
belkacem Ould said ◽  
Abderrahmane Aissa ◽  
Mohammed El Ganaoui
Keyword(s):  
Free Convection ◽  
Vertical Wall ◽  
Vertical Cylinder ◽  
Geometrical Parameters ◽  
Uniform Temperature ◽  
Governing Equations ◽  
Simpler Algorithm ◽  
Prandtl Numbers ◽  
Volume Method ◽  
Rayleigh Numbers

A transient two dimensional study of free convection in a vertical cylinder partially annulus is conducted numerically. Uniform temperature is imposed cross a vertical wall, while the top and bottom walls are adiabatic. The governing equations are solved numerically by using a finite volume method. The coupling between the continuity and momentum equations is effected using the SIMPLER algorithm. Solutions have been obtained for Prandtl numbers equal to 7.0, Rayleigh numbers of 103to 106and height ratios 0.5. The influence of physical and geometrical parameters on the isotherms, velocity fields, average Nusselt has been numerically investigated.

Numerical simulation of thermal convection in a two-dimensional finite box

1989 ◽  
Vol 199 ◽  
pp. 1-28 ◽  
Author(s):  
Isaac Goldhirsch ◽  
Richard B. Pelz ◽  
Steven A. Orszag
Keyword(s):  
Prandtl Number ◽  
Flow Patterns ◽  
Chaotic Regime ◽  
Two Dimensional ◽  
Onset Of Convection ◽  
Chaotic Flows ◽  
Chaotic Flow ◽  
Rayleigh Numbers ◽  
Pseudo Spectral ◽  
Rayleigh Benard

The problems of dynamical onset of convection, textural transitions and chaotic dynamics in a two-dimensional, rectangular Rayleigh-Bénard system have been investigated using well-resolved, pseudo-spectral simulations. All boundary conditions are taken to be no-slip. It is shown that the process of creating the temperature gradient in the system, is responsible for roll creation at the side boundaries. These rolls either induce new rolls or move into the interior of the cell, depending on the rate of heating. Complicated flow patterns and textural transitions are observed in both non-chaotic and chaotic flow regimes. Multistability is frequently observed. Intermediate-Prandtl-number fluids (e.g. 0.71) have a quasiperiodic time dependence up to Rayleigh numbers of order 106. When the Prandtl number is raised to 6.8, one observes aperiodic (chaotic) flows of non-integer dimension. In this case roll merging and separation is observed to be an important feature of the dynamics. In some cases corner rolls are observed to migrate into the interior of the cell and to grow into regular rolls; the large rolls may shrink and retreat into corners. The basic flow patterns observed do not change qualitatively when the chaotic regime is entered.

scholarly journals Testing the Magnetohydrodynamic Analysis Software with Natural Convection and Geodynamo Problems

2021 ◽  
pp. 6-13
Author(s):  
И. В. Бычин
Keyword(s):  
Natural Convection ◽  
Boundary Conditions ◽  
Numerical Solution ◽  
Control Volume ◽  
Benchmark Problems ◽  
Quick Method ◽  
Simpler Algorithm ◽  
Induction Equation ◽  
Hydromagnetic Dynamo ◽  
Volume Method

В рамках метода контрольного объема разработан программный код для численного решения задач неидеальной магнитной гидродинамики вязкой несжимаемой жидкости на структурированных разнесенных сетках в сферических координатах. При дискретизации уравнения индукции магнитного поля использован алгоритм ограниченного переноса (Сonstrained Transport Algorithm) и схема QUICK с методом отложенной коррекции для аппроксимации конвективных членов. Для решения уравнений гидродинамики использован алгоритм SIMPLER. Программный код разработан для моделирования естественной конвекции и гидромагнитного динамо во вращающемся шаре или сферическом слое. Представлены результаты решения тестовых задач естественной конвекции и геодинамо с вакуумными граничными условиями, демонстрирующие достаточно точное соответствие результатам эталонных расчетов. Программное обеспечение разработано для ускорителей вычислений, поддерживающих технологию CUDA, с использованием набора расширений к языку программирования Фортран.   Using the control volume method we developed the software for the numerical solution of viscous incompressible fluid resistive magnetohydrodynamics problems on structured staggered meshes in spherical coordinates. The constrained transport algorithm and the QUICK method with delayed correction for the approximation of the convective terms were used for the discretization of the magnetic field induction equation. The SIMPLER algorithm was applied to solving the hydrodynamic equations. We developed software for modeling natural convection and the hydromagnetic dynamo in a rotating sphere or spherical shell. We proposed an algorithm for the numerical solution of the geodynamo problem with vacuum boundary conditions. The results of solving natural convection and geodynamo benchmark problems with vacuum boundary conditions are presented; they demonstrate a fairly accurate agreement with the reference calculations. The software supports CUDA-enabled accelerators and uses a set of extensions to the Fortran programming language.

Heat Transfer Characteristics of the Single-Phase, Elbow Thermosyphon

1993 ◽  
Vol 115 (1) ◽  
pp. 173-177 ◽  
Author(s):  
G. S. H. Lock ◽  
D. Ladoon
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Thermal Performance ◽  
Single Phase ◽  
Flow Model ◽  
Flow Patterns ◽  
Heat Transfer Characteristics ◽  
Heated Section ◽  
Rayleigh Numbers

This paper describes the results of single-phase experiments on a right-angled, or elbow, thermosyphon with the cooled section upright and the heated section horizontal. For diameter-based Rayleigh numbers less than 107.6, the data indicate the existence of two flow regimes: fully mixed and impeded. A flow model is used to suggest how the cooled section and heated section flow patterns are coupled together. This model satisfactorily explains the effect of geometry on heat transfer, as revealed in the usual plots of Nusselt number versus Rayleigh number. Thermal performance was found to be comparable to that of the linear thermosyphon.

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