Flow developing properties of a compressible parallel jet

Qilin Liu,Huanxin Lai

doi:10.1063/5.0036662

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.

Highlights

It is widely accepted that large-scale structures, known as coherent structures, vortical structures, or eddies, govern the development of jet flows and are possible sources of jet noise radiation (Hileman et al, 2005; Jordan and Colonius, 2013; and Unnikrishnan et al, 2019)
An example is the experimental study of compressible round jets (Bridges, 2006), where the space–time correlations along the center and lip lines were measured by a particle image velocimetry (PIV) system, so the convection velocities of coherent structures were solvable
The central processing unit (CPU) time compared in the last row in Table I shows that the coherent-structure Smagorinsky model (CSM) is computationally more efficient than the localized dynamic Smagorinsky model (LDSM), the selective mixed scale model (SMSM), and the coherent-structure kinetic-energy model (CKM)

Summary

INTRODUCTION

It is widely accepted that large-scale structures, known as coherent structures, vortical structures, or eddies, govern the development of jet flows and are possible sources of jet noise radiation (Hileman et al, 2005; Jordan and Colonius, 2013; and Unnikrishnan et al, 2019). Scitation.org/journal/adv supersonic but along the entire lip-line was subsonic, which implied the possible presence of Mach waves. These studies have unveiled the variation in the convection velocity in the lateral direction of jet flows. The motion of vortices may change the flow signals in both time and space Such changes have been manifested by spatio-temporal modulations of amplitudes, as summarized by Cavalieri et al (2011) about the reported experimental studies. Cavalieri et al (2011) indicated that the pressure or velocity signals along the jet lip-line have a pattern of convected waves, and the signal amplitudes undergo modulations both in space and in time. The dominant frequency components of the pressure signals sampled in the vortical flow region are analyzed by the Fourier technique so as to unveil their propagation features

LES OF FLOW FIELD

Instantaneous vortical flow

Intermittency of vortical flow

Pressure signals in vortical flow regions

CONCLUSION