Flow developing properties of a compressible parallel jet

Abstract

Two-point space–time correlation and Fourier spectrum analysis are applied to large-eddy simulation results of a compressible parallel jet flow at Reynolds number 2000 and Mach number 0.9. Flow properties including instantaneous vortical structures, flow intermittency, convection velocity of vortical structures, and pressure signals in the near flow-field are presented and discussed. The results show multi-scale features of vortical structures after flow transition. High intermittency is found to occur around the outer edges of the shear layer and the region surrounding the potential core, where the motion of vortices is vigorous. In order to analyze the motion of vortices, the convection velocity of vortical structures in the center plane of the jet is calculated by a designed solution procedure. The high convection velocity zone is shown to be a “V” shaped cap covering the potential core. The pressure fluctuation signals in the vortical flow are analyzed so as to study the effects of vortex motion. The signals show the feature of wave-packets and contain multiple dominant frequencies. The distribution of the dominant frequencies is characterized by a terrace shaped zone with stairs descending in both the streamwise and lateral directions. In addition, the phase velocity of the pressure signals shown by the frequency–wavenumber diagram unveils that the pressure fluctuations travel at a stable phase velocity along the lip-line of the jet, while the component with a supersonic phase velocity is salient in the downstream of the flow transition region outside the shear layer.