Sweeping Jets Issuing From the Face of a Backward-Facing Step

Abstract

This study quantified the performance and fluid disbursal capabilities of several fluidic oscillator variations injecting from the face of a backward-facing step. These devices were designed as a replacement for a pair of nonoscillating fuel injector jets in an ultra-compact combustor. However, these results have relevance whenever fluid is injected from the face of a backward-facing step making the oscillator performance widely applicable. The oscillators were tested with and without coflow and at varying coflow velocities, which controlled the strength of the recirculation behind the backward-facing step. The fluidic oscillators investigated included single as well as paired oscillators that produced in-phase and out-of-phase synchronized jets. The injected fluid disbursal was found to be dependent on the velocity ratio of the freestream air and the injecting jet velocity. Additionally, the oscillation angle was found to be a function of Reynolds number due to the interaction of the oscillating jet with the walls of the models used in the present study. Finally, the oscillation frequency was found to be independent of Reynolds number, throat aspect ratio, working gas, and model scale, which resulted in a Strouhal number of 0.017. This result was supported by nondimensionalizing the published data from several other studies.