Mixing Characteristics of Elliptical Jets with Plug

It is known that elliptical jets entrain surrounding air more effectively than round jets. Past studies also show that convergent-divergent nozzles operated at overexpanded conditions create flow instabilities that enhance the jet mixing. A convergent-divergent passage can be created between an elliptical nozzle and a round plug. The exit-to-throat height of the annular passage is non uniform around the nozzle. The aim of the present study is to investigate the characteristics of this arrangement which is expected to produce vigorous mixing. The mean velocity fields of subsonic-speed jets from such nozzle configuration were surveyed using an array of Pitot probes. Comparisons were made between jets using elliptical nozzles with plug at various pressure and exit-to-throat area ratios and jets from round, convergent nozzles with plug. The results indicate that elliptical nozzles with plug split the flow in two cores. This increases the mixing and promotes faster velocity decay in the plume. The flow instabilities associated to overexpanded conditions in the nozzle also contribute to enhance the mixing.