Estimations of the grid size and computational cost for direct numerical simulation (DNS) and large-eddy simulation (LES) of Rayleigh-Bénard convection (RBC) are presented in the {Ra, P r} phase space. Computational requirements to reach the so-called asymptotic Kraichnan or ultimate regime of turbulence using DNS are far too expensive. Therefore, we turn to LES to predict the large-scale behavior at very high Ra-numbers. However, a priori alignment studies clearly show why the modelization of the SGS heat flux is the main difficulty that (still) precludes reliable LES of buoyancy-driven flows at (very) high Ra-numbers. This inherent difficulty can be by-passed by carrying out simulations at low-P r numbers where no SGS heat flux activity is expected. This opens the possibility to reach the ultimate regime carrying out LES of RBC at low-P r using meshes of 10101011grid points. Nevertheless, to do so, we firstly need to combine proper numerical techniques for LES (also DNS) with an efficient use of modern hybrid supercomputers.
Abstract
Estimations of the grid size and computational cost for direct numerical simulation (DNS) and large-eddy simulation (LES) of Rayleigh-Bénard convection (RBC) are presented in the {Ra, P r} phase space. Computational requirements to reach the so-called asymptotic Kraichnan [...]