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Characteristics of High Performance Ejectors

Report Number: AFWAL TR 81-3170
Author(s): J. E. Minardi
Corporate Author: University of Dayton Research Institute
Laboratory: Flight Dynamics Laboratory
Date of Publication: 1982-01-01
Pages: 99
Contract: F33615-81-K-3017
Project: 2404
Task: 240410
AD Number: ADA118720

The use of ejectors in energy conversion processes and thrust augmentation requires that the mixed flow be produced at a high efficiency. Although many definitions of efficiency have been used to describe the efficiency of an ejectors, we have used an efficiency based on thermodynamic availability which is referenced to the stagnation properties of the secondary flow (the flow being 'pumped'). As is well known, a compressible-flow, control-volume approach to analyzing a constant area ejector yields two solutions: one with a subsonic mixed flow and one with a supersonic mixed flow. The supersonic mixed flow produces the best efficiencies and highest total pressures. The properties of the supersonic mixed flow are of necessity related to the properties of the subsonic mixed flow by the normal shock relations. Nonetheless, in practice, the subsonic mixed flow is, in general, not achieved through a normal shock (or pseudo-normal shock) from the supersonic mixed flow solution. A model is presented that gives a physical interpretation to the various solutions obtained from the mathematics, and more importantly, some fundamental limits are presented and a procedure is developed for determining the efficiency that can be achieved in a constant area ejector when the mixed flow is supersonic.

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