Acoustic field and flow characteristics of supersonic impinging jet and source features

This study focuses on the noise characteristics and source distribution of supersonic impinging jets， aiming to clarify the noise generation mechanisms and their relationship with jet velocity according to the nth power law. Experiments were conducted in an anechoic chamber， utilizing high-frequency PIV and a far-field arc array to measure the flow field and sound field of the impinging jet. Vortex structures were identified based on the Ω and Q criteria， and the relationship between vortex characteristics and discrete tones was analyzed. The overall sound pressure level （OASPL） of the impinging jet was monitored at downstream， midstream， and upstream directions， with monitoring angles （β=30°， β=80°， and β=120°） to investigate the relationship between OASPL and jet velocity based on the nth power law， and to compare the variations in discrete tones with St=0.61 and St=0.33 under different nozzle pressure ratio （NPR） and nozzle-plate distance （L/d）. After removing discrete tones， the OASPL conforms well to the nth power law with jet velocity. The velocity exponents at different monitoring angles were found to be 7.8 （β=30°）， 7.0 （β=80°）， and 10.8 （β=120°）， indicating the differences in noise source characteristics at different monitoring angles. Further analysis revealed significant correlations between OASPL， discrete tone amplitude， and jet velocity gradient. Vortex identification using the Ω and Q criteria revealed a strong vorticity region downstream of the third to fifth shock cell in the potential core， which coincides with the main noise source location of the screech tone， thus achieving a visualization of the noise source. Phase analysis showed that at NPR=2.37， the vortex pair structure in the flow field correlates positively with the discrete tone intensity of St=0.33， while at NPR=2.84， the strong vortex region on the downstream side of the impinging jet correlates positively with the discrete tone intensity of St=0.61. This study reveals the power-law relationship between the OASPL of supersonic impinging jet noise and jet velocity， and confirms a significant correlation between noise source location and strong vortex regions under different monitoring angles and St conditions. Vortex identification using the Ω and Q criteria confirmed the consistency between the primary noise source regions within the potential core of the impinging jet and the screech tone， enabling the visualization of noise source locations.