Experimental study of the noise suppression of supersonic impinging jets with chevrons

Supersonic impinging jets may cause many adverse ground effects, including surface erosion, nonuniform surface heat transfer, lift loss, and acoustic loading. In this study, chevron nozzles are used to suppress the noise generation of supersonic impinging jets originated from a circular convergent nozzle with the jet Mach number of 1.2. An array of microphones is used to measure the far-field acoustic fields, and a schlieren system is employed to measure the near-field flow structures. Three impinging distances are considered to examine the differences between the impinging jets and the free jet, and to assess the effect of impinging distance on the noise characteristics. Two chevron nozzles with different penetration angles are designed to investigate the potentials of chevron nozzles in controlling the supersonic-impinging-jet noise. Results show that the chevron nozzles do not alter the directivity of overall sound pressure levels, but significantly reduce the amplitude at all emission angles. The discrete tones in the impinging jets are dramatically mitigated or eliminated, and the levels of broadband noise are also significantly reduced over a wide range of frequency band, regardless of the impingement distance. The influences of chevrons on the near-field flow structures are checked with the root-mean-square values and proper orthogonal decomposition of schlieren images, which provide more evidence on the noise suppression mechanism with chevrons.