離散周波数をもつジェット騒音の研究 : 第1報,騒音特性と発生機構

抄録

The powerful jet noise containing discrete frequencies have been studied for the subsonic jet issuing from a nozzle with exit divergent angle. The discrete frequency noise was discussed to clarify the noise characteristics and generation mechanism. A series of moving eddies near the exit of the nozzle were visualized by means of the instantaneous Schlieren method and high-speed video camera. The power spectrum of noise was distinguished by the appearance of a number of high peaks, and the frequencies of these peaks became integral multiples of the fundamental frequency. The fundamental frequency was classified into three discontinuous stages accompanying hysteresis upon increase and decrease in pressure. By digital image processing, it was clarified that the fundamental frequency of noise agreed with the generation frequency of eddies, and the eddies flowed out from the nozzle exit successively, keeping the distance between two eddies constant.