Analysis of the characteristic acoustic tones of an impinging jet

The acoustic emission of a supersonic jet is an interesting and fundamental issue due to the several technological applications and the diverse physical aspects to be still clarified. An experimental analysis of the characteristic acoustic tones of a supersonic impinging jet has been carried out with a particular attention on the effect of the nozzle pressure ratio and the distance of the impinging surface. The screech tones, typical of an imperfectly expanded supersonic free jet, have been first investigated to have an idea of the deflection from the free jet behavior due to the impinging surface. Then the analysis has been focused on smaller distances of the impinging plate from the jet exit to evaluate the behavior of the impinging tones. The difference between screech and impinging tones, due to the different interactions in the generating feedback mechanism, has been observed.