The Effect of Expansion on Large Scale Structure Evolution in a Compressible Turbulent Boundary Layer

摘要

The effects of four expansion regions (centered and gradual (R/ delta _0 approx = 50) expansions of both 7 deg and 14 deg) on the large scale structure of an incoming fully-developed Mach 3 turbulent boundary layer were investigated. Filtered Rayleigh scattering and double-pulse visualizations were made possible by the presence of scalar water condensation in the freestream and its absence in the boundary layer. Spatial correlations show the increase in scale of the large scale structures across the 7 deg centered expansion is commensurate with the increase in boundary layer thickness. Spatial correlations at s/ delta _0 approx = 10 downstream of the 7 deg centered expansion show the structure angle is similar to that of the flat plate. Ensembles of plan views were used to study the elongated longitudinal structures found previously in these flows.