The Structure of Normal-Shock/Turbulent-Boundary-Layer Interactions Modified by Mass Removal

The effect of mass removal on nominally two-dimensional, normal- shock/turbulent-boundary-layer interactions was investigated experimentally. The flowfield had a freestream approach Mach number of 1.49 and a Reynolds number based on boundary layer momentum thickness of 14,600. Distributed mass removal was imposed over a length of approximately 40 initial displacement thickneses, the entire bleed zone being located immediately upstream of the shock. Detailed velocity field information was obtained for two flows, using a two component laser Doppler velocimeter system. The two time mean velocity components and the three Reynolds stress components were determined. Measurements were extended over both supersonic and subsonic regions. Surface pressure information was also obtained. The removed mass flow, averaged over the length of the bleed zone, was 2.5% and 8% of the freestream mass flow, for the two cases investigated. The data indicate that the mass removal initiates an oblique expansion wave at the leading edge of the bleed zone, increasing the Mach number of the normal shock. The expansion wave intersects the shock, initiating a weak shear layer in the subsonic flow. The boundary layer thickness remains approximately constant over the bleed zone. The streamwise velocity at the perforated plate is high, close to the freestream velocity. Turbulence intensity downstream of the bleed zone is comparable to the intensity of the approach boundary layer, in contrast to uncontrolled interactions in which the turbulence intensity is greatly amplified. Keywords: Transonic flow, Two dimensional flow, Mass transfer, Supersonic inlets.