Compressibility and structure of turbulence in supersonic shear flows

Abstract

In this paper, different aspects of supersonic turbulent flows are discussed, in connection with some properties of compressible turbulence. The discussion is based on experiments, in which particular features have been found. The first point is the influence of density gradients. It is shown that changing the density gradient in a boundary layer does not change the particularly small size of the energetic scales. This effect is attributed to compressibility and not to density stratification, probably by modifying the `inactive motions'. The second point is about the importance of acoustics in a mixing layer. The results show that turbulent transport of momentum and heat follows the same analogy as in boundary layers, and that the energy losses by acoustic radiation are too weak to explain the reduction of the spreading rate, which is the major global effect of compressibility.