Oscillation mode of pressure on inner wall of cylinder on which underexpanded jet impinges

Abstract

This study experimentally investigated a radially spreading underexpanded jet impinging on the inner wall of a cylindrical object. When an underexpanded jet impinges on a flat object, the jet oscillates and radiates high-frequency noise. For this reason, studies have been conducted on rectangular or axisymmetric jets impinging on flat plates, which have shown a relation between noise and self-induced oscillation. However, not enough research has been done on radial jets impinging on inner wall of a cylindrical object. Therefore, the purpose of this study is to investigate the relationship between noise and vibration, as well as the characteristics of the pressure oscillation, in the case of radial jets. The jet issued from a convergent radial nozzle composed of a pair of circular tubes with a diameter D. The cylindrical object used for pressure measurement had an inner diameter D_a. The inner wall of object was equipped with eight pressure measurement holes evenly spaced in the circumferential direction, allowing for pressure measurements using transducers. Measurements of the jet's wall pressure and sound pressure levels were taken. The experiments were conducted by varying the nozzle pressure ratio from 2.0 to 4.8 in increments of 0.2. The results revealed that pressure oscillation and sound pressure levels varied at the same fundamental frequency in each condition. Furthermore, in a flow field where three shock cells were formed, the frequency at which pressure oscillations propagated circumferentially around the object was found to be about half of the fundamental frequency.