Convection velocity in a supersonic turbulent boundary layer

This paper describes the measurement of convection velocities in a Mach 3 boundary layer using streamwise-separated hot wires. The broad-band convection velocity, determined from space-time correlations, is 0.9U_∞ across the entire outer region of the boundary layer. The convection velocity was decomposed into frequency components using cross-spectral techniques. These average results reveal that large-scale motions convect more rapidly than small-scale motions in the lower part of the boundary layer, but not in the outer part. Convection velocities were also calculated for individual large-scale structures by means of a conditional sampling technique. The resulting distribution indicates that the majority of the large-scale structures convect at nearly the same velocity. The similarity of the present results with previous measurements taken over a wide range of Reynolds numbers and Mach numbers suggests the existence of a 'universal' convection velocity profile.