円形先細ノズルから噴出される噴流の放射音に関する研究

抄録

An experimental study was conducted on a transonic jet impinging on a flat plate. When a jet impinges on a flat plate, it generates a high-frequency noise called a screech, which causes oscillations in the flow field. In this study, focusing on the screech generated by a phenomenon called feedback loop, the frequency and sound pressure of a jet exhausted from a circular converging nozzle were measured using a microphone. The jets issued from a circular converging nozzle of diameter D. Experiments were conducted by varying the distance l from the nozzle to the plate and the ratio of pressure in the high-pressure tank to atmospheric pressure. From the obtained low frequencies of sound, the values of the coefficients related to the advection velocity of the disturbance were calculated. Using these coefficients, theoretical values were calculated and compared with the low frequency values obtained in another experiment. The comparison showed that the two values are very close, and this is the fundamental frequency of the screech. The reason for the discrepancy between the theoretical value and the experimental ones shown at certain conditions may be that the location of the plate shock wave moved from the expansion region to the compression region, resulting in a lower frequency.