Experimental and Computational Investigation of the Effect of Swirling Flows on an Ejector With Cut Angled Entraining Diffuser

Abstract

This research project compared the performance of two subsonic air-air ejectors with multi-ring entraining diffusers. The first ejector system was investigated by Qi Chen in his thesis. It consists of a nozzle, mixing tube, and a Full Entraining Diffuser. The Full Entraining Diffuser was found to cause drag forces in an airplane because it protrudes out of the engine cowling. In order to make a streamline fit in the engine cowling, the Full Entraining Diffuser needs to be cut. The second ejector system was then designed by the author to investigate the effect of cutting the diffuser on a 30o incline on the performance of the ejector. This study involves experimental and numerical investigation on how cutting the diffuser affects the performance of the ejector. The experiments were conducted at the Hot Gas Wind Tunnel (HGWT) at Grant Timmins Lab. Both ejector systems were tested, but the Ejector with Full Diffuser was only tested under 20o inlet swirl condition to compare with Chen’s experimental data. Four different inlet swirls (0o, 10o, 20o, and 30o) were applied on the Ejector with Cut Angled Diffuser. Numerical studies using Computational Fluid Dynamics (CFD) were also conducted for both ejector systems. Gambit 2.4.6 and Fluent 6.3.26 were used to generate mesh and run the CFD simulations for all cases. The numerical studies were conducted to conclude which flow features CFD can or cannot predict and how important they are in terms of predicting the overall ejector performance (pumping, pressure recovery, velocity and temperature distributions at the diffuser outlet). The experimental results showed that the inlet swirl had similar effect on the Ejector with Cut Angled Diffuser to the Ejector with Full Diffuser. In general, cutting the diffuser on a 30o incline does not affect the overall performance of the ejector. For the CFD simulations, RNG k-ε with Enhanced Wall Function was found to give reasonable prediction on the bulk flow properties, such as total pumping, pressure recovery in the diffuser, wall temperature, and velocity profiles at the diffuser outlet.