Ejector-Nozzle Flow and Thrust

Abstract

An analysis for predicting the secondary and primary flows and the thrust coefficient of ejector nozzles is presented. Particular attention is given to the diverging shroud ejector in which the throat of the secondary stream is formed at a small distance down-stream of the primary nozzle exit; i.e., near the plane of the minimum shroud area. The basic assumption in the analysis is that the shroud is sufficiently short so that the mixing of the two streams is incomplete, and that both streams have isentropic cores. The momentum thickness of the mixing region is obtained from the momentum-integral equation for the turbulent mixing region assuming that momentum and temperature diffuse at the same rate. The momentum thickness at the nozzle exit is related to the initial momentum thickness created by the wall separating the two streams. The exit-momentum thicknesses of the mixing region and the wall are used to obtain the actual thrust coefficient. Experimental data on primary-secondary flow properties and thrust coefficients of a divergent-shroud ejector nozzle show good correlation with the theory.