Identification and visualization of coherent structures in rayleigh-bénard convection with a time-dependent RANS

Abstract

A time-dependent Reynolds-average-Navier-Stokes (TRANS) method is applied to capture and analyze the large-scale coherent structure in Rayleigh-Benard (RB) convection over a flat and wavy bottom wall at a range of Rayleigh numbers. The method can be regarded as a Very Large Eddy Simulation (VLES) in which the unresolved random motion is modelled using a low-Re-number k-e-b² algebraic stress/flux single-point closure model. The large scale motion, which is the major mode of heat and momentum transfer in the bulk central region, is fully resolved by the time solution. In contrast to LES, the contribution of both modes to the turbulent fluctuations are of the same order of magnitude. The approach was assessed by comparison with the Direct Numerical Simulations (DNS) and experimental data using several criteria: visual observation of the large structure morphology, different structure identification criteria, and long-term averaged mean flow and turbulence properties. A visible similarity with large structures in DNS was observed, confirming the suitability of TRANS approach to reproduce the flows dominated by large coherent motions.