Mixing characteristics of an underexpanded multiple jet ejector

A study of the mixing characteristics of an underexpanded multiple jet ejector is presented. Results obtained using schlieren flow visualization pitot tube and hot wires are discussed. The parameters varied were: nozzle pressure ratio, ejector area ratio, ejector throat to nozzle exit plane distance, and the number and spacing of the jets. Performance characteristics derived from ejector exit plane velocity distributions have been drawn for two area ratios. In addition, a fair reference base for comparison of results has been established, by conducting identical tests on an equivalent single jet ejector. Results show that there is little difference between the two ejectors at subsonic conditions of operation. However, at underexpanded discharge conditions, a compact multiple jet ejector is distinctly superior. Mixing characteristics are better in such an ejector, even though the acoustic effects responsible for mixing in a single jet are almost insignificant. The location of the ejector throat has a strong effect on the ability of the ejector to entrain the ambient fluid. The best performance is obtained for the location closest to the nozzle exit. The number and spacing of the jets do not have a significant effect for the range of values studied.