The turbulence structure of a reattaching axisymmetric compressible free shear layer

The reattachment of a supersonic, axisymmetric shear layer downstream of a blunt-based afterbody is studied. Of primary interest are the effects of the "extra" strain rates, such as bulk compression, concave streamline curvature, and lateral streamline convergence associated with shear layer reattachment on the structure of the turbulence field. Experimental turbulence data obtained throughout the reattachment region with a two-component laser Doppler velocimeter are presented. In general, the axisymmetric compliant boundary reattachment process is shown to be different in character compared to the planar solid wall case. Most notably, significant reductions in the Reynolds stresses occur through the reattachment region due to the dominating effect of lateral streamline convergence as the flow approaches the axis. Similar to the planar solid wall case, however, a reduction in the mean turbulent transport toward the axis in the reattachment region was found, which suggests a radial containment of the large-scale eddies near the axis of symmetry. The reattachment process was also seen to have profound effects on the large-scale structures in the shear layer, primarily through reduced structural organization as indicated by instantaneous shear angle histograms.