The present experiments explore the influence of external asymmetric helical excitation on structural and mixing characteristics of the gaseous jet in crossflow (JICF). Helical forcing is applied via an array of speakers flush mounted around the exterior of the jet exit in the injection wall of the wind tunnel. The speakers are individually operated, allowing for controlled directional azimuthal forcing about the jet exit, for example, in counterclockwise or clockwise directions, and with variable amplitudes and frequencies. There is a special focus here on a high jet-to-crossflow momentum flux ratio (e.g., J = 41), which are known to have a convectively unstable upstream shear layer (USL) and to create asymmetric cross-sections with typically poorer mixing characteristics, Acetone planar laser induced florescence (PLIF) imaging shows that asymmetric forcing at frequencies near the fundamental frequency associated with the USL can greatly influence jet cross-sectional structure. In many cases such forcing creates enhanced symmetrization of the counter-rotating vortex pair (CVP), more typical of jets with an absolutely unstable USL, with associated improvement in molecular mixing.
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