Effect of boundary layer thickness on transverse sonic jet mixing in a supersonic turbulent crossflow

The surface boundary through which a sonic jet in supersonic cross flow is injected is shown to have a significant effect on the size, penetration, and mixing characteristics of the jet plume. A circular, high-pressure, sonic jet is injected into a M = 3.4 supersonic crossflow through a well-characterized turbulent boundary layer of two different thicknesses (δ/d = 0.6 and 6.1), with variable momentum ratios (J = 1.2, 2.6, and 5). Planar laser Mie scattering of condensed ethanol droplets is used to quantitatively image the injected fluid concentration in both side and end-views at multiple downstream locations. Jet penetration, plume area, and characteristic size and location of regions of intense mixing are compared. The jets injected through the thicker boundary layer are shown to have significantly enhanced jet penetration (∼50%), spread (∼100%), and mixing intensity (∼100%, especially in the near-field) over a wider area of the jet plume. Additionally, characterization of mixing is examined using the variance in the concentration field as well as probability density functions of concentration determined along contours of constant jet fluid concentration. From these results, the jet injections associated with the thicker boundary layer transition from shear dominated mixing zones on the windward side to more distributed mixing zones throughout the plume at earlier downstream locations and show influence of interactions between boundary layer vorticity and vortical structures within the jet leading to larger lateral expansion.