抄録
The present paper describes an experimental work to investigate a noise phenomenon in over-expanded supersonic jets that are discharged from a convergent-divergent nozzle. When the convergent-divergent nozzle runs at low nozzle pressure ratios, the shock wave occurs within the divergent section of the nozzle. The noise phenomenon of a jet flow is generated by an emission of strong acoustic tones due to the unsteadiness of the shock wave. In order to specify the flow noise of a jet, acoustic measurements are performed to obtain the overall sound pressure level and noise spectra. The results obtained show that unlike the frequency of the screech tone due to the shock-cell structures in the jet flow, the frequency of the acoustic tone due to the shock wave within the nozzle somewhat increases with an increase in the nozzle pressure ratio, and the acoustic tones take place in two stages.
