Effect of Boundary Layer Thickness on Jet Mixing in a Supersonic Turbulent Crossflow

Abstract

The upstream injection surface boundary layer is shown to have a significant effect on the mixing characteristics of a sonic jet in supersonic cross flow. A circular, high-pressure, sonic jet is injected into a M=3.5 supersonic crossflow through different boundary layer thicknesses (δ /D = 6.2 and 0.6), with variable momentum ratios (J = 2, 5, and 10). Planar Laser Mie Scattering of condensed ethanol droplets is used to quantitatively image the injected fluid concentration in both side and end-views. Jet fluid concentrations probability distribution functions are constructed to better understand the mixing dynamics. These PDFs are integrated to create mixed fluid fraction profiles and determine the total amount of mixed fluid. Mixing quantities are computed on different spanwise planes to determine if centerline mixing efficiencies are characteristic of the entire three-dimensional flow. Through these analyses, thick boundary layers are shown to significantly enhance the jet penetration and spread, but do not alter the jet mixing capabilities, regardless of momentum ratio or position within the jet.