円筒内壁に衝突する放射状に広がる不足膨張噴流の放射音に関する研究

抄録

An underexpanded jet radiates noise and oscillates when the jet impinged on the object. These phenomena, the radiated sound and oscillation patterns, depends on the shape of the nozzle and the object that is impinged. In this study, an underexpanded radial jet impinged on an inner wall of a cylinder. Visualization experiment using the shadowgraph method confirmed a strong density change due to the jet impingement. The location where the density wave was generated was analyzed. Therefore, it was estimated that the location was the cylinder end. Acoustic measurement confirmed several dominant frequency components. These frequency components are integer multiples of the fundamental frequency component. The impinging jet and flow pattern are analyzed using the formula of the relationship between the convection velocity of disturbance and the screech. The location of the density wave estimated through visualization is considered to be the sound source. We analyzed the frequency of the feedback loop that forms when disturbances interfere with this sound source. Therefore, oscillations at two and three times the fundamental frequency coexist in the flow field of a radial jet. It is also inferred that these oscillations affect a single frequency component. Thus, these are strongly related to the flow patterns of impinging jet and wall jet.