Effects of upstream pipe length on pipe-cavity jet noise

An experimental study is carried out to quantify the acoustic radiation of underexpanded pipe-cavity jet noise. Pipe-cavity configurations with different upstream pipe lengths are studied over a range of Mach numbers. Detailed acoustic measurements such as frequency analysis, sound pressure levels, directivity, and acoustic power analysis are carried out to show the effect of upstream pipe length. Finite element simulations are carried to predict the resonance frequencies of the pipe-cavity. Results of simulation with zero mean flow condition match well with theoretical results and the present experiments. The far-field acoustic spectrum exhibits strong cavity tones and shock associated noise. The results show that the pipe-cavity resonates close to the combined tangential-longitudinal mode. The increase in shear layer thickness tends to attenuate the cavity tones, with a small increase in screech tonal noise. An increase in upstream pipe length leads to a decrease in overall sound pressure levels and acoustic power.