A study of the supersonic ejector–diffuser system with an inlet orifice

Abstract

Supersonic ejectors are simple mechanical components, which generally perform mixing and recompression of two fluid streams. Ejectors have found many applications in engineering. In aerospace engineering, they are used for high altitude testing (HAT) of a propulsion system by reducing the pressure of a test chamber. It is composed of three major sections: a vacuum test chamber, a propulsive nozzle, and a supersonic exhaust diffuser. This paper aims at the improvement in HAT facility by focusing attention on reducing exhaust back flow into the test chamber, since alteration of the backflow appears as one of the potential means of significantly improving its performance. The simplest backflow-reduction device was an orifice plate at the duct inlet, which would pass the jet and entrained fluid but impede the movement of fluid upstream along the wall. Results clearly showed that the performance of the ejector–diffuser system was improved for a certain range of system pressure ratios, whereas the orifice plate was detrimental to the ejector performance for higher-pressure ratios. It is also found that, there is no change in the performance of diffuser with an orifice at its inlet, with respect to its pressure recovery. Hence, an appropriately sized orifice system should produce considerable improvement in the ejector–diffuser performance in the intended range of pressure ratios.