The Counter-Current Shear Layer Analogy for Transverse Jets of Differing Geometries

This experimental study investigates upstream shear layer (USL) instabilities of a jet in crossflow for a variety of jet injector geometries. Prior work demonstrates that an improved analogy of a counter-current shear layer (CCSL), applied to the USL of a flush-nozzle injected equidensity transverse jet, can approximate whether the USL is convectively or absolutely unstable. The extension of this analogy to alternative jet injector geometries, including an elevated nozzle, tabbed flush nozzle, coaxial nozzle-generated jet, and flush round pipe, is explored. USL spectral measurements and PIV-based POD are used to determine the state of the USL instability. POD mode coefficient plots demonstrate qualitative consistency with spectral measurements in denoting convective or absolute instabilities. Velocity profiles and momentum thicknesses evaluated at the leading edge of the jet reveal good agreement between USL transition and CCSL critical velocity ratios predicted from theory. The CCSL analogy is found to be very robust in predicting USL transition, though it begins to fail for flush pipe-generated jets with a parabolic velocity profile and a diminished resemblance to counter-current shear layer phenomena.

Supported by AFOSR Grant FA9550-19-1-0191, NSF Grant CBET-1933310, and CAPES