A Numerical Investigation Of Turbulent Natural Convection In A 3-D Enclosure Using K- Sst Model And Piso Method

ABSTRACT

In turbulent natural convection transport mechanism, fluid motion is generated by buoyancy-induced density gradients resulting from internal body forces due to heating. The objective of this study was to conduct a numerical investigation of turbulent natural convection in a 3-D cavity using the k- SST model and the PISO method. The problem being investigated was computational study of turbulent natural convective flow using a primitive variable to solve time averaged momentum equation instead of using the vorticity-vector potential formulation. The statistical-averaging process of the mass, momentum and energy governing equations introduces unknown turbulent correlations into the mean flow equations namely Reynolds stress ( ) and heat flux ( ), which were modeled using k- SST model. The RANS equations, energy and k- SST turbulent equations were first non-dimensionalized and the resulting equations were discretized using Finite Volume Method and solved using PISO and SIMPLEC algorithms. Second order upwind was set for the momentum and energy discretization equations. The residuals convergence criterion was such as to reduce the absolute residuals below of for energy and for continuity, momentum and k- SST turbulent equations. The solutions are presented at Rayleigh number of , an Aspect Ratio of 0.5 and Prandtl of air of 0.71. The results were then validated using experimental benchmark results. The results showed that use of PISO method improves convergence time and speed, improves computational effort per unit time, absolute error in the solution of flow variables diminishes faster, the Pressure term is solved and as a result, profiles for wall shear stress and static pressure have been obtained and convective heat transfer is more significant than conduction in turbulent natural convection in a 3-D cavity. The velocity and thermal profiles obtained are important for thermal comfort, efficiency of energy balance and the effectiveness of the ventilation system when modeling air flow in buildings.