SCRAMJET NOZZLE EXPERIMENT WITH HYPERSONIC EXTERNAL FLOW

An experimental study of scramjet asymmetric nozzle flowfields is conducted to investigate the effects on nozzle performance of interactions between engine exhaust and hypersonic external flow. The test model consists of a flat-plate ramp and a short cowl. Tests are performed in a hypersonic wind tunnel (M is-proportional-to = 7.1) whose freestream constitutes the external flow around an aerospace plane. Room temperature air is used to simulate engine exhaust flow. Model surface pressure and pitot pressure distributions in the flowfields are measured, from which nozzle performance is calculated. Flow visualizations are performed using several techniques. It is found that in underexpansion conditions, the external flow affects the model surface pressure only from the ramp sides because the intercepting shock (barrel shock) does not impinge upon the ramp surface. It is shown that the external flow produces an effect which suppresses boundary-layer separation on the ramp surface. When using a long side fence (SF), spanwise expansion of the exhaust flow is restrained, thus, a slight pin of thrust can be obtained relative to that using a shorter side fence. The predicted nozzle performance by the two-dimensional method of characteristics with boundary-layer correction agrees well with the long side fence experimental results.