Effects of Tabbed-Nozzle on Pumping Performance of Incompressible Short Mixer–Ejector

Abstract

The effects of tab number and tab orientation angle on the pumping performance for an incompressible short air-to-air mixer–ejector equipped with tabbed primary nozzle were experimentally explored. The incorporated mixing duct was designed in a straight type with a typical area ratio (mixing duct to primary nozzle) of 3.06 and length-to-diameter ratio of 0.8. Simultaneously, a numerical computation was also carried out on the simulation of mixing flowfields to reveal the trends and differences observed in the tabbed mixer–ejector measurements. The results confirm that the streamwise vortices created by the tabs cause an improvement in mixing efficiency, leading to greater values of pumping for a short air-to-air mixer–ejector. By comparing with the baseline case of confluent nozzle, the eight-tab nozzle increases the pumping ratio by approximately 75%. This value is about 50, 30, and 15% for the six-tab, four-tab, and 12-tab nozzles, respectively. It is also found that the tabbed primary nozzle with tab orientation angle of 135 deg is capable of entraining the maximum amount of ambient air into the mixing duct. In the range between 90 and 135 deg, tab orientation angle seems have a weak influence on the ejector pumping performance. However, an obvious reduction in ejector pumping ratio occurs under the large tab orientation angle of 150 deg. For an incompressible short air-to-air mixer–ejector, it is concluded that more intense streamwise vortices would produce stronger mixing and thus lead to a larger pumping ratio.