S0506-3-3 Buoyancy effects on turbulence structures in a horizontal plane channel. : Reynolds-number dependence

Abstract

Direct numerical simulations of fully developed turbulent flows in a horizontal plane channel heated from below are performed at low bulk Richardson numbers Ri<0.01 to examine buoyancy effects on turbulence structures. It is found that streamwise and wall-normal RMS velocities are increased by the effect of buoyancy in plane Couette flow at low Reynolds number Re = 400 and in plane Poiseuille flow at Re=2000, 3000, 4000. In larger- Re Couette turbulence (Re=750, 2000), on the other hand, only the streamwise RMS velocity is observed to be significantly intensified. In the former case the spanwise length scale of buoyancy-induced flow is close to that of near-wall streamwise vortices, leading to the enhancement of the wall-normal velocity fluctuation, while in the latter they are separated and thus no significant enhancement occurs.