Mixing of a sonic transverse jet injected into a supersonic flow

The mixing characteristics of an underexpanded sonic jet injected into a Mach 1.6 crossflow are studied experimentally. Shadowgraph photography and planar laser-induced fluorescence from acetone are used to obtain temporally resolved flowfield visualizations of a side view of the barrel shock region, a side view of the downstream plume, and an end view cross section of the plume. Instantaneous images, mean and standard deviation images, and image-intensity probability density functions (PDFs) are used to study the mixing produced by large-scale turbulent structures. PDFs show that time-averaged mixture fraction measurements greatly overestimate the actual level of instantaneous mixing in the flowfield. Comparisons of the instantaneous images and PDFs show the role of large-scale rolling structures and jetlike plumes in transporting coherent packets of fluid across the three-dimensional shear layer formed between the jet and crossflow. Significant instantaneous mixing in this flowfield occurs in the wake region downstream of the barrel shock region and below the jet centerline. The counter-rotating streamwise vortex pair in the jet plume plays an important role in the scalar mixing processes because it transports jet fluid down toward the wake and entrains crossflow fluid from below up into the jet.