The characteristics and evolution of large‐scale structures in compressible mixing layers

Single‐ and double‐pulsed visualizations were employed to study the characteristics and evolution of large‐scale structures in compressible mixing layers with convective Mach numbers (Mc) of 0.51 and 0.86. Instantaneous images and spatial correlations based on large ensembles of images show that large‐scale structures which span the entire mixing layer thickness are a more dominant feature at Mc=0.51 than at Mc=0.86. Double‐pulsed images in the Mc=0.51 developing region show the structures’ formation to proceed as the roll‐up of a wavy mixing region, in agreement with the Kelvin–Helmholtz picture of structure formation derived from studies of incompressible mixing layers. However, little indication of roll‐up was present for Mc=0.86. In the Mc=0.51 fully developed region, the large‐scale structures evolve similarly to those of incompressible mixing layers, even undergoing pairing processes. Similar structure evolution processes were not encountered in Mc=0.86; instead, it was more difficult to even track ...