Acoustic Measurements of High-Temperature Supersonic Impinging Jets in Multiple Configurations

This study investigated the acoustic characteristics of a Mach 1.5 jet at various temperatures impinging on a flat surface in three geometric configurations: 1) normal impingement, 2) oblique impingement, and 3) jet blast deflector impingement. Near-field and far-field microphone measurements were made at fixed locations relative to the nozzle in all three configurations, and in the jet blast deflector configuration, unsteady pressure measurements were obtained on the deck surface near the base of the jet blast deflector. It was found that discrete impingement tones are generated in the normal impingement configuration at small nozzle-plate distances. For oblique and jet blast deflector impingement, while no tones are present at lower jet temperatures, elevated jet temperatures lead to the generation of tones, suggesting that changes to the impinging flow field as a result of higher jet temperature make it more susceptible to resonant behavior. The maximum unsteady loads on the deck surface occur at large impingement distances that are relevant to the jet blast deflector application. These high unsteady loads are speculated to be a result of (i) the redirected flow from the impingement surface, (ii) flow entrained in the main jet shear layer as the jet spreads, and (iii) the grazing wall jet produced by the interaction between the main jet shear layer and the deck surface. Overall, these results provide valuable information on some aeroacoustic properties of impinging jets in configurations useful from an application as well as fundamental perspective.