VARIABLE DENSITY MIXING UNDER VARIABLE MEAN PRESSURE GRADIENT

etc15 Tracking Number 122

Turbulent mixing of a heterogeneous mixture of two incompressible, miscible fluids with different densities is investigated by using Direct Numerical Simulations (DNS). The mixing occurs in response to stirring induced by buoyancy-generated motions, in a triply periodic (1024^3) domain subjected to acceleration, g. The acceleration starts as positive and is reversed (g<0) or changed to neutral (g=0) during the flow evolution. These are unit problems that aim to mimic the core of the mixing layer of acceleration driven Rayleigh-Taylor (RT) and shock-driven Richtmyer-Meshkov (RM) instabilities and are also useful for verification and validation of mix models. The flow starts from rest and, for g>0, there is an initial growth of turbulence followed by turbulence decay as the fluids become molecularly mixed. The acceleration is changed at the peak of the Favre averaged turbulent kinetic energy (TKE). When compared to the constant gravity case, acceleration reversal causes a faster decay of total kinetic energy of the system and replaces larger structures with well-mixed small structures. The transition of energy from large to small scales and the dependence of mixing on the acceleration switch are investigated for Atwood numbers ranging from 0.05 to 0.9. In addition, the decay law for the g=0 case, corresponding to anisotropic, variable density turbulence decay and relevant to the RM problem is also examined.