An experimental investigation on effect of ambient flow on aerodynamic performances of an external nozzle

Abstract

For space plane with air-breathing engines, equipping Single Expansion Ramp Nozzle on its aft-body is beneficial for thrust augmentation. The cowl of this nozzle is truncated (thus, termed as an external nozzle), in order to reduce its weight, friction drag, and cooling requirement, and also to attain pressure recovery (so-called altitude compensation) on the ramp wall by the impingement of pressure waves generated by the interference between external nozzle flow and ambient flow on ramp wall surface, in case of over-expanded condition. The present study is to evaluate the effects of ambient flow on the external nozzle flow field, as little research has been conducted to elucidate the effects. Room temperature nitrogen gas was injected to simulate air-breathing engine exhaust in cases without and with ambient flow at a supersonic semi-free jet wind tunnel. A straight expansion ramp was employed as the external nozzle. Pressure distributions on the ramp wall were measured and results without and with ambient flow were compared. Comparison showed that presence of ambient flow reduced the magnitude of ramp wall pressure induced by the impingement of pressure waves, and thus, the strength of pressure waves generated by the interference. Flow characterization by pressure wave tracking showed that spatial variation in ambient flow pressure caused this weakening of the incident pressure wave upon the ramp surface. Thus, altitude compensation effect in the over-expanded condition became smaller than that without ambient flow.

Keywords

• wind tunnel test
• supersonic flow
• nozzle flow
• altitude compensating nozzle
• ambient flow