Planar fluorescence imaging of a supersonic axisymmetric base flow with mass bleed

Acetone planar laser-induced fluorescence (PLIF) was used to study the supersonic flow over an axisymmetric base with mass bleed. Detailed side-view and global end-view images were obtained in the recirculation regions, shear layer, and trailing wake. For the three bleed rates studied, the instantaneous behavior of the flowfield deviated substantially from the expected mean flow, especially for bleed rates below the optimal case. Large pockets of unmixed bleed fluid dominated the flowfield for the low and intermediate bleed rates, even in the trailing wake, highlighting the unsteady nature of the flowfield. The power-on condition for the high-bleed-rate case was the most temporally stable flowfield, due to the high momentum of the bleed jet. A multiplateau stirring effect was prevalent for all cases, consistent with previous compressible shear layer findings, and the effect increased with increasing bleed rate and distance downstream. Probability density functions (PDFs) of PLIF intensity indicated a similar mixing character between the low and intermediate bleed rates in the near wake and for all bleed rate cases in the trailing wake. The multiplateau stirring effect and unmixed bleed fluid pockets were represented well in the mixing PDFs.