Design and Test of a Hypersonic Isentropic-Spike Intake with Aligned Cowl

Abstract

A study of reexpansion scramjet intakes is presented. Reexpansion intakes employ mixed external-internal compression with the internal contraction fixed by starting requirements and a cowl aligned with the external flow to minimize intake contribution to vehicle drag. As a result of the starting limitation, the captured flow is partially reexpanded, resulting in nonuniform flow at the intake exit. Stream thrust averaging was used to determine equivalent one-dimensional flow for input to a scramjet engine cycle analysis. Engine performance increases with compression, and thus optimum turning-angle appears to be at the limit for detachment of the internal cowl shock. An axisymmetric reexpansion intake was built using stereo lithography and tested at Mach 7.1 in the University of Oxford gun tunnel. The stream-thrust-averaged properties were determined experimentally from measurements of axial force and mass capture. Schlieren and surface-pressure measurements were taken. Skin friction in the model isolator section was found to significantly affect intake performance, increasing the amount of compression and reducing efficiency. Starting characteristics were determined experimentally in QinetiQ’s High Density Tunnel.