Abstract: High Atwood number effects on buoyancy-driven variable-density turbulence
Non-Boussinesq effects on turbulent mixing of a heterogeneous mixture of two incompressible, miscible fluids with different densities are investigated in terms of properly normalized L^(2m)-norms of density gradient by using high-resolution Direct Numerical Simulations. In a triply periodic domain (up to size 2048^3), the mixing occurs in response to stirring induced by buoyancy-generated motions between two fluids which are initially segregated in random patches. During the flow evolution, the density gradient can reach high values even at low Atwood numbers indicating that non-Boussinesq effects play a crucial role within the flow. The results cover a broad range of Reynolds numbers ( Re) and non-dimensional density ratios (Atwood numbers, A) including small ( A= 0.05), moderate (A= 025 and 0.5), and high (A= 0.75) values. It is found that the density gradient is much larger in regions of light fluid compared to regions occupied by the heavier fluid, indicating a strong mixing asymmetry between light and heavy fluids at high Atwood number.