抄録
The present paper describes the effect of duct length on acoustic characteristics of over-expanded jet which are discharged from convergent-divergent nozzle. A duct made of annular metal was installed at the nozzle exit and varied in length from 0 and 6D. A Schlieren optical system is used to visualize detailed jet structures. Acoustic measurement is performed to obtain noise spectra. The results obtained show that 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. The duct devices suppress the acoustic tone and the screech tone.
