Density Effects on Turbulent Kinetic Energy and Stress Budgets in Shear-Driven Mixing Layers

Direct Numerical Simulations of low-speed shear-driven mixing layers involving two streams of fluids with different densities reveal that the interface grows preferentially into the stream of lighter density. This effect strengthens as the density difference increases, with very little growth occurring into the heavy stream as the density difference (i.e., Atwood number) becomes large. Accompanying the interface growth, the turbulent kinetic energy and stresses are more intense in the light fluid. A suite of incompressible temporal simulations were performed involving two miscible fluids, with Atwood numbers of up to 0.87 in large domains of up to 6144 x 2048 x 1536 grid points. To explain the drift of intense turbulence to the light-fluid side, the effects of differing densities on the budgets of the turbulent kinetic energy and Reynolds stress components are analyzed. Dominant terms (production, transport, and dissipation) remain similar to those of the single-density case but become asymmetric, while additional variable-density terms appear and begin to make appreciable contributions at the highest Atwood numbers analyzed.