Direct numerical simulation of compressible flow over a backward-facing step

In this paper, we perform a direct numerical simulation study to investigative the effect of compressibility on the flow over a backward-facing step. A spectral multidomain method is used for simulating the compressible flow at Reynolds number of 3000 over an open backward-facing step. The role of compressibility in the sub-sonic regime is studied by simulating the flow at different free-stream Mach numbers. We analyze the effect of compressibility on the averaged flow and the Reynolds stresses. Results indicate that the effect of compressibility on the separated and reattached shear layer in the backward-facing step is different from that on spatial and temporal mixing layers studied 1 previously. While the canonical free shear flows exhibit a reduction in growth rate with increase in Mach number, the shear layer in the present study shows an opposite trend. We compute the budget of turbulent kinetic energy to determine the plausible causes of such behavior. We conclude that a greater turbulence production for higher Mach numbers is primarily responsible for the larger growth rate of the shear layer.