scholarly journals Numerical study of the effects of natural convection in a thermoacoustic configuration

2019 ◽  
Vol 20 (8) ◽  
pp. 807
Author(s):  
Omar Hireche ◽  
Catherine Weisman ◽  
Diana Baltean-Carlès ◽  
Virginie Daru ◽  
Yann Fraigneau
Keyword(s):  
Porous Medium ◽  
Natural Convection ◽  
Numerical Study ◽  
Three Dimensional ◽  
Boussinesq Approximation ◽  
Acoustic Resonator ◽  
Operating Conditions ◽  
Temperature Fields ◽  
Convection Flow ◽  
Conductivity Anisotropy

This study focuses on natural convection flows within a cylindrical guide containing a porous medium. This configuration is applicable to standing-wave thermoacoustic engines, usually composed of an acoustic resonator where a (short) stack (or porous medium) is inserted, with a heat exchanger placed at one of its ends. The resulting horizontal temperature gradient, when high enough, triggers the onset of an acoustic wave. Natural convection effects are usually neglected in thermoacoustics so that axisymmetry is often assumed. Here a 3D numerical study of natural convection flow is performed using a finite volume code for solving mixed Navier-Stokes and Darcy-Brinkman equations under Boussinesq approximation. The influence of the porous medium’s physical characteristics (permeability, thermal conductivity, anisotropy) on the flow and temperature fields is investigated. It is shown that such flows are fully three-dimensional and therefore can modify significantly starting as well as steady operating conditions of the thermoacoustic engine.

Solar Radiation Assisted Natural Convection in Uniform Porous Medium Supported by a Vertical Flat Plate

1997 ◽  
Vol 119 (1) ◽  
pp. 89-96 ◽  
Author(s):  
A. J. Chamkha
Keyword(s):  
Porous Medium ◽  
Natural Convection ◽  
Solar Radiation ◽  
Flat Plate ◽  
Boussinesq Approximation ◽  
Incident Radiation ◽  
Temperature Fields ◽  
Convection Flow ◽  
Local Similarity ◽  
Vertical Flat Plate

Natural convection flow of an absorbing fluid up a uniform porous medium supported by a semi-infinite, ideally transparent, vertical flat plate due to solar radiation is considered. Boundary-layer equations are derived using the usual Boussinesq approximation and accounting for applied incident radiation flux. A convection type boundary condition is used at the plate surface. These equations exhibit no similarity solution. However, the local similarity method is employed for the solution of the present problem so as to allow comparisons with previously published work. The resulting approximate nonlinear ordinary differential equations are solved numerically by a standard implicit iterative finite-difference method. Graphical results for the velocity and temperature fields as well as the boundary friction and Nusselt number are presented and discussed.

Visualization and Prediction of Natural Convection of Water Near Its Density Maximum in a Tall Rectangular Enclosure at High Rayleigh Numbers

2000 ◽  
Vol 123 (1) ◽  
pp. 84-95 ◽  
Author(s):  
C. J. Ho ◽  
F. J. Tu
Keyword(s):  
Natural Convection ◽  
Vertical Wall ◽  
Three Dimensional ◽  
Temperature Fields ◽  
Convection Flow ◽  
Oscillatory Convection ◽  
Uniform Temperature ◽  
Density Maximum ◽  
Rectangular Enclosure ◽  
Rayleigh Numbers

An experimental and numerical investigation is presented concerning the natural convection of water near its maximum-density in a differentially heated rectangular enclosure at high Rayleigh numbers, in which an oscillatory convection regime may arise. The water in a tall enclosure of Ay=8 is initially at rest and at a uniform temperature below 4°C and then the temperature of the hot vertical wall is suddenly raised and kept at a uniform temperature above 4°C. The cold vertical wall is maintained at a constant uniform temperature equal to that of the initial temperature of the water. The top and bottom walls are insulated. Using thermally sensitive liquid crystal particles as tracers, flow and temperature fields of a temporally oscillatory convection was documented experimentally for RaW=3.454×105 with the density inversion parameter θm=0.5. The oscillatory convection features a cyclic sequence of onset at the lower quarter-height region, growth, and decay of the upward-drifting secondary vortices within counter-rotating bicellular flows in the enclosure. Two and three-dimensional numerical simulations corresponding to the visualization experiments are undertaken. Comparison of experimental with numerical results reveals that two-dimensional numerical simulation captures the main features of the observed convection flow.

A Pseudospectral Analysis of Laminar Natural Convection Flow and Heat Transfer Between Two Inclined Parallel Plates

2006 ◽  
Author(s):  
Serkan Kasapoglu ◽  
Ilker Tari
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Boundary Conditions ◽  
Boussinesq Approximation ◽  
Temperature Fields ◽  
Convection Flow ◽  
Parallel Plates ◽  
Natural Convection Flow ◽  
Constant Wall Temperature ◽  
Laminar Natural Convection

Three dimensional laminar natural convection flow of and heat transfer in incompressible air between two inclined parallel plates are analyzed with the Boussinesq approximation by using spectral methods. The plates are assumed to be infinitely long in streamwise (x) and spanwise (z) directions. For these directions, periodic boundary conditions are used and for the normal direction (y), constant wall temperature and no slip boundary conditions are used. Unsteady Navier-Stokes and energy equations are solved using a pseudospectral approach in order to obtain velocity and temperature fields inside the channel. Fourier series are used to expand the variables in × and z directions, while Chebyshev polynomials are used to expand the variables in y direction. By using the temperature distribution between the plates, local and average Nusselt numbers (Nu) are calculated. Nu values are correlated with φ, which is the inclination angle, and with Ra·cosφ to compare the results with the literature.

Natural Convection in a Porous Medium Bounded by a Long Vertical WavyWall and a Parallel Flat Wall

2010 ◽  
Vol 65 (10) ◽  
pp. 800-810 ◽  
Author(s):  
Ambrish K. Tiwari ◽  
Ashok K. Singh
Keyword(s):  
Porous Medium ◽  
Nusselt Number ◽  
Natural Convection ◽  
Numerical Study ◽  
Temperature Fields ◽  
Wavy Wall ◽  
Heat Flows ◽  
Flat Wall ◽  
Porous Region ◽  
Parallel Wall

This paper presents natural convection in a porous medium bounded by a long vertical wavy wall and a parallel wall. The shape of the wavy wall is assumed to follow a profile of cosine curve. The wall is kept at a constant heat flux while the parallel wall is kept at a constant temperature. The governing systems of nonlinear partial differential equations in their non-dimensional form are linearised by using the perturbation method in terms of amplitude and the analytical solutions for velocity and temperature fields have been obtained in terms of various parameters occurring in the model. A numerical study of the analytical solution is performed with respect to the realistic fluid air in order to illustrate the interactive influences of governing parameters on the temperature and velocity fields as well as skin friction and Nusselt number. It is found that in the case of maximum waviness (positive and negative), the velocity component along the wall has a reverse trend near the flat wall. It is observed that the parallel flow through the channel at zero waviness is greater than at maximum waviness (positive and negative) while the same trend occurs for perpendicular flow in the opposite direction. Examination of the Nusselt number shows that in the presence and absence of a heat source, the heat flows from the porous region towards the walls but in the presence of a sink, the heat flows from the walls into the porous region.

scholarly journals Influence of thermal radiation on non-Darcian natural convection in a square cavity filled with fluid saturated porous medium of uniform porosity

2012 ◽  
Vol 17 (2) ◽  
pp. 223-237 ◽  
Author(s):  
Tapas Ray Mahapatra ◽  
Dulal Pal ◽  
Sabyasachi Mondal
Keyword(s):  
Porous Medium ◽  
Natural Convection ◽  
Thermal Radiation ◽  
Horizontal Plane ◽  
Vertical Wall ◽  
Temperature Fields ◽  
Staggered Grid ◽  
Convection Flow ◽  
Physical Parameters ◽  
Square Cavity

Influence of thermal radiation on natural-convection flow in a square cavity filled with a porous medium of uniform porosity having isothermal vertical walls and adiabatic horizontal walls, has been studied numerically by using finite-difference method with staggered grid distribution. The simulation is performed by considering both Darcian and non-Darcian models. Governing momentum and energy equations are solved numerically to obtain velocity and temperature fields for various values of different physical parameters. It is seen that increasing the thermal radiation parameter enhances the local Nusselt number on the left vertical wall whereas the reverse effects are observed due to increase in the heat generating parameter when Ra = 109. The temperature at the mid-horizontal plane decreases with increase in the value of Rayleigh number up to a certain distance from the left vertical wall and beyond that distance the opposite trend is observed. The temperature at the mid-horizontal plane increases with increase in the value of heat generating parameter.

Numerical Study of 3D Nonlinear Disturbance Growth in Transitional Natural Convection

2010 ◽  
Author(s):  
Tilek Aberra ◽  
Steven W. Armfield ◽  
Masud Behnia ◽  
Shigenao Maruyama ◽  
Atsuki Komiya
Keyword(s):  
Natural Convection ◽  
Numerical Study ◽  
Three Dimensional ◽  
Intermediate Stage ◽  
Convection Flow ◽  
Mean Flow ◽  
Sequence Of Events ◽  
Dimensional Boundary ◽  
Perturbation Parameters ◽  
Disturbance Growth

Three dimensional boundary layer disturbance growth in natural convection adjacent to a uniformly heated vertical plate has been studied using a finite volume direct numerical simulation (DNS). The sequence of events associated with the intermediate stage of the spatial laminar-turbulent-transition for water, with Prandtl number Pr = 6.7, for the Rayleigh numbers in the range Rax ≈ 1 × 1010 – 4 × 1013, with perturbation parameters closely matching the experiment reported in [1], is investigated. Preliminary calculations confirm that this stage is characterized by the development of spatially periodic inner and outer span-wise vortices (shear layers), which travel in a differing fashion and speed; and a secondary mean flow system. The important route to natural convection flow breakdown, the arising of a double vortex mean longitudinal system, repeatedly suggested by past experiments, seems to be related to the complex and opposing behavior of these two layers.

Numerical Study of Interaction Between Natural Convection Flow and Horizontal Wind

2007 ◽  
Author(s):  
S. Sakai ◽  
Y. Watanabe
Keyword(s):  
Heat Flux ◽  
Natural Convection ◽  
Large Scale ◽  
Numerical Study ◽  
Air Flow ◽  
Three Dimensional ◽  
High Heat ◽  
Horizontal Wind ◽  
Convection Flow ◽  
And Behavior

When a large-scale fire, such as a town area fire by an earthquake disaster and forest fire, happens, there can be a fire whirlwind, which is a strong flow including strong flame and sparks. It is sometimes called a firestorm. Fire whirlwind is exposed to high heat, and possesses high heat itself. Therefore, the fire whirlwind is very dangerous. The whirlwind moves and promotes spread of a fire and may enlarge the damage rapidly. Various studies are performed about fire whirlwind, but the property and outbreak mechanism of the whirlwind are not elucidated enough till now. Therefore, in this study, we pay our attention to the flow that is a basic phenomenon of fire whirlwind, and examine the influence that a natural convection gives to outbreak and behavior of fire whirlwind by numerical computation. The numerical analysis performed three-dimensional calculation with analysis software FLUENT6.1. Firstly, a model of the fire domain is constructed. The model is referred from an example of large-scale fire at the Great Kanto Earthquake (1923 in Japan), and natural convection is observed for different heat flux. Then, it is analyzed in a similar model whether a whirlwind occurs or not, after natural convection is fully-developed with changing velocity of the air flow from the side. Furthermore, it is analyzed in a model in which a fire occurs at random whether a whirlwind occurs or not after natural convection is fully-developed with changing velocity of the air flow from the side. As a result of analysis, a whirlwind occurs. The whirlwind sometimes moves and extinct. Then, the influence that a natural convection gives outbreak of the whirlwind is evaluated with changing heat flux and velocity of wind.

EXPERIMENTAL AND NUMERICAL STUDY OF THREE-DIMENSIONAL NATURAL CONVECTION AND FREEZING IN WATER

1994 ◽  
Author(s):  
C. Abegg ◽  
Graham de Vahl Davis ◽  
W.J. Hiller ◽  
St. Koch ◽  
Tomasz A. Kowalewski ◽  
...  
Keyword(s):  
Natural Convection ◽  
Numerical Study ◽  
Three Dimensional

THREE-DIMENSIONAL NATURAL CONVECTION IN A POROUS MEDIUM ENCLOSED WITH CONCENTRIC INCLINED CYLINDERS

1982 ◽  
Author(s):  
Yasuyuki Takata ◽  
K. Fukuda ◽  
Shu Hasegawa ◽  
Kengo Iwashige ◽  
H. Shimomura ◽  
...  
Keyword(s):  
Porous Medium ◽  
Natural Convection ◽  
Three Dimensional
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