Flow structure identification in the near wake of a supersonic separated flow using FAEMD

The supersonic separated flowfield aft of a blunt-faced cylinder aligned with the freestream is highly complex such that a technique able to identify instantaneous turbulent structure within it is valuable. In this study, multi-dimensional extensions of fast and adaptive empirical mode decomposition (FAEMD) are implemented on both three-component planar and volumetric velocity fields of said flowfield, obtained using particle image velocimetry. The resulting two-dimensional intrinsic mode functions revealed the various length scales associated with different regions of the flowfield. Coherent streamwise-oriented structures of different scales were detected throughout the flowfield that indicate the presences of quasi-streamwise vortices. The presence of sharply angled structures, at about 45º to the local flow direction, suggests that both conventional-and counter-hairpin vortices are present within the flowfield, especially in the recompression zone and trailing wake.