Behavior of Vortices Moving in the Vicinity of Supersonic Jet

Abstract

An underexpanded jet is one of supersonic jets. The jet becomes underexpanded when the pressure ratio exceeds the critical value across the convergent nozzle discharging it. The jet is not uniform because of the presence of the expansion wave, the compression wave and the shock wave formed in it. In the jet boundary, many vortices are generated by the shearing stress between the supersonic flow of jet and still atmosphere. The interaction of vortices and jet is closely related to the high frequency sound radiating from such flow field. The high frequency sound is called Screech Tone. This Screech Tone has been studied extensively and its relationship to the vortex has been discussed. However, measurement methods are still not established for vortex moving in the vicinity of the jet boundary. In this study, the vortex moving in the vicinity of the jet was experimentally examined. The device consisting of a laser and an optical sensor was applied to measure the vortex. The vortex was measured at several points around the jet and frequency and time differences between points were investigated. The flow field was visualized using optical methods. And the high frequency sound emitted from the flow field is measured using a microphone.