Turbulent structures in a supersonic three-dimensional blunt-body wake

The near wake of a blunt-base cylinder at 10° angle-of-attack to a Mach 2.46 freestream flow is studied using Mie scattering flow visualization at several locations along the shear layer and trailing wake. Three-dimensional effects cause a septum of high-speed fluid to appear in the plane investigated, significantly altering the structure of the near wake as compared to that for axisymmetric base flow. The individual images show a variety of large-scale turbulent structures, with the structures in general becoming larger but less organized during and after recompression. Autocorrelation analysis shows that the average structures grow substantially during recompression and become more inclined with respect to the freestream during reattachment. The average structures are elliptical through reattachment, but become deformed in the developing wake. Analysis of the variations in the transverse position of the shear layer (flapping) indicate that the flapping grows monotonically as the shear layer develops, with RMS values ranging from 8-31% of the local shear layer thickness. The thickness peaks during recompression at 22% of the base radius. The interface convolution also peaks during recompression. Flapping of the septum shear layer is similar to that for the main shear layer, but both the thickness and interface convolution are lower for the septum shear layer than for the main shear layer. The significant interface convolution of the septum indicates that it has the potential to actively entrain fluid from the recirculation region, which may explain the low base pressure for this three-dimensional flow compared with that for axisymmetric base flow.