Abstract
In this study, flow characteristics are experimentally and numerically discussed, especially concerning shock-cell structure and oscillatory phenomena of supersonic jet. The jet becomes underexpanded when the nozzle pressure ratio of convergent nozzle exceeds the critical value. The underexpanded jet is not uniform because of the presence of the expansion wave, the compression wave and the shock wave formed in it. Many vortices are induced in jet boundary region by shearing stress generated between supersonic jet flow and atmospheric air. They interact with shock waves composing cell node of jet, which is closely related to a noise radiating from the jet. In experiment, flow field is visualized and the shape of cell structure is examined. Furthermore, frequency of vortex generation is measured. The jet is simulated using TVD scheme and the results are compared with the experimental ones. Distortion of cell structure caused by three dimensional oscillation of jet and behavior of vortices are discussed.
Highlights
Many vortices are induced in jet boundary region by shearing stress generated between supersonic jet flow and atmospheric air
They interact with shock waves composing cell node of jet, which is closely related to a noise radiating from the jet
Underexpanded jet is one of the supersonic jets; when the nozzle pressure ratio of the convergent nozzle is higher than the critical value, the jet is underexpanded
Summary
Underexpanded jet is one of the supersonic jets; when the nozzle pressure ratio of the convergent nozzle is higher than the critical value, the jet is underexpanded. The expansion waves, which are generated at the nozzle lip, propagate in the jet and reflected at jet boundary as the compression waves. Such a flow field is often observed in the assist gas of laser cutting [1], the cooling jet of glass tempering process [2,3] and the exhaust jet of VSTOL aircraft or rocket. The flow field causes several issues, for example, behavior of jet disturbed by vortex of the jet boundary and high frequency noise generation called “screech tone” [4,5,6,7]. Under the same conditions, the numerical study was carried out using TVD scheme
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