Performance enhancement of a ramjet air intake by passive bleed of boundary layer

Wind-tunnel tests were carried out to study the effect of passive boundary-layer bleed on the aerodynamic performance of an isolated two-dimensional ramjet air-intake model in the Mach number range 1.8 to 3.0. Backpressure at the exit of the model was controlled by varying the exit area of the intake. Passive bleed of the internal boundary layer was created by displacing the side walls between the ramp and cowl, to bypass viscous flow into ambient condition. Measurements included steady static pressure distributions on the intake ramp, cowl, side plate, total pressure recovery, and mass flow rate. Results indicate that, although any gap improves the total pressure recovery and the mass flow rate, a gap of 1.6 mm (corresponding to increase in the local width of intake) or capture area up to bleed plane by 8.5% provides the best overall efficiency, considering these parameters, and postpones the supercritical range of the intake. The overall performance of the intake significantly improved due to alleviation of shock-wave and boundary-layer interactions in the intake. © 2018 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.