Numerical investigation of the effects of Helmholtz resonator and primary flow oscillations on subsonic ejector performance

This paper investigates the effect of a Helmholtz resonator with one or two pairs of deep cavities on the mixing chamber of a subsonic ejector to determine its impact on the ejector's entrainment ratio. The study utilizes numerical analysis, where the depth, location, and number of cavities were varied while keeping the width of the resonator constant. The Fluent software solved the Unsteady Reynolds-Averaged Navier-Stokes equations with the k- εturbulence model. The presence of the cavity at the beginning, middle, and end of the mixing chamber reduced the entrainment ratio by 0.6%, 3.8%, and 6.6%, respectively, and the presence of the second cavity at the positions of 20, 40, and 60 mm with respect to the first cavity reduced the entrainment ratio by 9.9%, 10.1%, and 10.2% respectively. The depth effect was studied at a distance of 20 mm for a pair of cavities at depths of 75, 100, and 125 mm causing a reduction of 4.9%, 9.9%, and 13.1% in entrainment ratio. The study also observed longitudinal and pulsating oscillations inside the mixing chamber due to the simultaneous filling and emptying of opposite cavities. Furthermore, the amplitudes of the pressure oscillations in the first pair were weaker than those in the second pair. In the final part of the research, the effect of primary flow fluctuation was also investigated, the results of which showed that the primary flow fluctuation increases the entrainment ratio by 5.2% due to the increase of effective mixing between the primary and secondary flow.