On the convection velocity of turbulent structures in supersonic shear layers

Abstract

An ansatz, complemented by appropriate selection rules, is proposed to estimate the convection velocity U_c of turbulent vortical structures in supersonic shear layers. The proposed scheme assumes that, for supersonic convective Mach numbers, shocks will form in one of the two shear layer free streams. The strength of the shocks is estimated by assuming that the flow configuration is stationary with respect to perturbations in the mean flow quantities caused by the turbulent fluctuations. Given the shock strength, the convection velocity U_c, and the associated convective Mach numbers are calculated by matching the estimated total pressure at the stagnation points in the convected frame. The data indicate a convection velocity U_c that is close to that of one of the free streams. That appears to be well accounted for by the proposed scheme, which also suggests that the flow can undergo large jumps in configuration with small changes in the flow parameters. This has important implications for supersonic mixing and hypersonic propulsion applications.