Wake topology in a three-dimensional supersonic base flow

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. Large-scale structures are active in the shear layer emanating from the windward and lateral parts of the separation corner but not from the leeward separation corner. Autocorrelation analysis shows that the average structures grow substantially in side views during recompression. The average structures are elliptical through reattachment, but become deformed in the developing wake. Analysis of the shear layer flapping indicates that the flapping grows monotonically as the shear layer develops. The interface convolution peaks during recompression. The highest convolution before reattachment is found in the windward 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. End-view images show that the overall flapping of the wake centroid is relatively small. The structures in end-view images are largest in the windward shear layer and increase in size as the shear layer develops. The structures are aligned radially in end-view images on the symmetry plane but are inclined in the lateral plane, indicating windward-to-leeward circumferential flow. Global interface convolution analysis shows a peak shape factor after reattachment, at the same location as the peak shape factor in the side-view images of the lateral plane.