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 crosse ow are studied experimentally. Shadowgraph photography and planar laser-induced e uorescence from acetone are used to obtain temporally resolved e owe eld visualizations of a side viewof 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 e owe eld. Comparisons of the instantaneous images and PDFs show the role of large-scale rolling structures and jetlike plumes in transporting coherent packets of e uid across the threedimensional shear layer formed between the jet and crosse ow. Signie cant instantaneous mixing in this e owe eld occursin the wakeregiondownstream ofthebarrel shock region and below thejetcenterline.Thecounter-rotating streamwisevortex pairin thejetplumeplaysan importantrole in the scalarmixing processes becauseit transports jet e uid down toward the wake and entrains crosse ow e uid from below up into the jet.

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