Darioush Gohari Barhaghi

Natural convection boundary layer in a 5:1 cavity

The natural convection boundary layer in a tall cavity with an aspect ratio of AR=5 is studied numerically. The Rayleigh number based on the width of the cavity is RaW=4.028×108. The large eddy simulation method together with different subgrid scale models are used to study the near-wall behavior of the boundary layer and the turbulence structure. It is found that the dynamic subgrid scale model is the most accurate model in terms of predicting the transition location. Results also indicate that the conventional grid resolutions expressed in viscous units that are used for forced convection flows are not appropriate in the case of the natural convection flows and higher grid resolutions are necessary. The turbulence statistics are studied in both the turbulent and the transition regions. Although the results of the fully turbulent region show no important grid dependency, it is found that the accuracy of the results in the transition region is highly grid dependent, suggesting that the subgrid scale fluct...

On the Validity of the Boussinesq Approximation in a Developing Mixed Convection Boundary Layer

In order to study the effect of the Boussinesq approximation and finding the temperature difference criterion for which it is valid, the fluid flow and heat transfer are studied in a vertical channel. The governing equations are solved considering two approaches namely Boussinesq approximation with constant fluid properties and Favre averaged equations with variable properties for the fluid. Large eddy simulation together with a dynamic subgrid scale model is employed as the numerical method. The working fluid is air and a constant heat flux boundary condition is applied to one of the channel walls while the other wall is kept insulated. The Grashof and Reynolds numbers based on the wall heat flux and the channel width are Gr=9.4middot107 and Re=5080. Since the hot wall temperature is high and the channel walls have a view factor close to unity, radiation is also taken into account and it is shown that about 10% of the heat is transferred via radiation

LARGE EDDY SIMULATION OF NATURAL CONVECTION BOUNDARY LAYER ON A CYLINDER

Large eddy simulation of natural convection boundary layer along a constant temperature vertical cylinder is studied and the results are compared with the existing experimental data. The highest local Grashof number is Gr_z=5*10^{11}. It is shown that although there are some discrepancies between the results in the region close to the wall, there is qualitative agreement between them. In order to verify the credibility of the simulations, cross correlation of Reynolds stresses is studied and interpreted.