Velocity measurements in the near-field of supersonic planar turbulent wakes

Results are presented from PIV measurements in a supersonic planar turbulent wake at M_∞ ≈ 3 to examine effects of compressibility in supersonic turbulent shear flows. This paper focuses on near-field measurements of the wake, for which the local relative Mach number Mr remains sufficiently large for compressibility effects to be potentially significant. In previous studies by these authors (Nakagawa & Dahm 1999, 2000) which examined entrainment and mixing properties in the far-field by using PLMS along with conventional pitot probe pressure measurements. Those results showed similar scaling properties in the far field as seen in incompressible wakes, but were unable to access the near-field region under M_∞ ≈ 3 conditions. Here we compare PIV results in the near-field at M_∞ ≈ 3 using two different PIV measurement approaches, one of which seeds the wake fluid only, and the other which also seeds the freestream fluid as well. A novel type of seeding particles is used in the current PIV system with superior properties over conventional microparticles. Results from instantaneous vortical structures allow an increased understanding of the mechanism of compressibility effects on entrainment and mixing in the near-wake region.