MEASURED THRUST LOSSES ASSOCIATED WITH SECONDARY AIR INJECTION THROUGH NOZZLE WALLS

The experimental program discussed herein addressed the aerodynamic effects of auxiliary air injection on the thrust of a scaled two-dimensional converging/diverging nozzle. The tests were intended as a means of validating certain analytical and computational fluid dynamics (CFD) models for the thrust loss associated with cooling air injection. The ratios of injected flow rate to mainstream flow rate employed are typical of those used to cool the internal surfaces of high-performance jet aircraft nozzles. The primary purpose of the investigation was to establish a data base of nozzle performance sensitivity to various secondary air injection parameters. Divergent section pressure distributions obtained in the presence of injection across the flaps indicate that the injected flow constricts the primary flow thus reducing its effective expansion ratio. The results obtained also show a definite dependence of performance on the angle at which the secondary air is injected. The thrust coefficient changes resulting from injection, relative to the ''no injection'' situation, were reasonably predicted by a simple one-dimensional formulation corrected for certain two-dimensional flow effects. This formulation was observed to apply for in injected flow rates up to about 6% of the primary now rate.