Discrete tones generated by the impingement of a high-speed jet on a circular cylinder

Abstract

Experimental measurements were made of the frequencies of discrete tones emanating from high subsonic and choked underexpanded jets of air issuing from a circular nozzle and impinging on a slender circular cylinder placed normal to the jet axis. In the experiments, a few types of discrete tones were observed. It is proved that the frequencies of the discrete tones can be calculated by using a feedback model proposed by Powell, and Ho and Nosseir. Schlieren photographs of the flow field along with the near-sound field were taken for various nozzle-to-cylinder distances and various pressure ratios. Close investigation of these schlieren photographs has shown that for the subsonic jet, one strong sound wave is emitted near the cylinder and two large ring vortices are produced near the nozzle exit during one cycle of the feedback loop. These two large ring vortices merge together in a later stage of the loop. For the choked underexpanded jet, one strong sound wave is emitted and one large ring vortex is produced during one cycle of the feedback loop. In this case, a merging of the successive large ring vortices has not occurred.