URANS and LES computations for the heat transfer characteristics of wall bounded buoyant flows

The present investigation provides an insight on the heat transfer characteristics of a differentially heated square cavity at a high Rayleigh number (= 10¹¹) through the use of advanced URANS models and a wall-resolved Large Eddy simulation (LES). The performance of the cost-effective RANS, using high-Reynolds-number (HRN) as well as low-Reynolds-numbers (LRN), turbulence closures is assessed. The models include both eddy-viscosity schemes and a second-moment closure which either fully resolve the viscous sublayer or adopt a recently developed numerical variant of the Analytical Wall Function (AWF) to approximate the wall shear stress and heat flux. Further, a computationally demanding wall-resolved LES is compared against the time-dependent 3D RANS simulations which enhances understanding on the transition phenomenon in the flow and provides an indication on the grid resolution requirements at such a high Rayleigh number.