Measured thrust losses associated with secondary air injection through nozzle walls

Abstract

The experimental program discussed herein addressed the aerodynamic effects of auxiliary air 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 parameters. Divergent section pressure distributions obtained in the presence of 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 injected flow rates up to about 6% of the primary flow rate. Nomenclature A = area Cd = discharge coefficient Q = coefficient used to modify one-dimensional stream thrust