AN INTERFEROMETRIC STUDY OF ORGANIZED STRUCTURES IN WAKES OF CIRCULAR-CYLINDERS

Double-pulse, diffuse-illumination interferometry has been used to stu dy the organized structures in the wake of a circular cylinder (M=0.6, Re-d=300,000). The interferograms show striking similarities to the f low visualization pictures of the incompressible wakes of circular cyl inders as obtained by other investigators. In particular, the interfer ograms taken with very short pulse intervals show concentrations of fi ne scale turbulence in the von Karman vortices and the existence of st reamwise vortices between these counter-rotating large-scale vortices. The fact that most of the features observed in low speed wakes using a variety of techniques can be observed in the interferograms illustra ted the potential of interferometry for the study of turbulent structu res in compressible flows.