Journal of Applied Fluid Mechanics (Jan 2019)
Large Eddy Simulation of Compressible Parallel Jet Flow and Comparison of Four Subgrid-Scale Models
Abstract
Large eddy simulations of a three-dimensional (3D) compressible parallel jet flow at Mach number of 0.9 and Reynolds number 2000 are carried out. Four subgrid-scale (SGS) models, namely, the standard Smagorinsky model (SM), the selective mixed scale model (SMSM), the coherent-structure Smagorinsky model (CSM) and the coherent-structure kinetic-energy model (CKM) are employed, respectively, and compared. The purpose of the study is to compare the SGS models and to find their suitability of predicting the flow transition in the potential core of the jet, and so as to provide a reference for selecting SGS models in simulating compressible jet flows, which is a kind of proto-type flow in fluid dynamics and aeroacoustics. A finite difference code with fourth-order spatial and very low storage third-order explicit Runge-Kutta temporal schemes is introduced and employed for calculation. The code, which was previously designed for simulating shock/boundary-layer interactions and had been widely validated in simulating a variety of compressible flows, is rewritten and changed into parallelized using the OpenMP protocol so that it can be run on memory-shared multi-core workstations. The computational domain size and the index of LES resolution quality are checked to validate the simulations. Detailed comparisons of the four SGS models are carried out. The results of averaged flow-field including the velocity profiles and the developments of shear-layer, the instantaneous vortical flows and the viscous dissipation, the predicted turbulence statistics and the balances of momentum equation are studied and compared. The results show that although the normalized developed velocity profiles are well predicted by the four SGS models, the length of the potential core and the development of the shear-layer reveal that the SM has excessive SGS viscosity and is therefore too dissipative to correctly predict the flow transition and shear-layer expansion. The model smears small vortical scales and lowers down the effective Reynolds number of the flow because of the over-predicted SGS viscosity and dissipation. The turbulence statistics and the balances of momentum equation have also confirmed the excessive dissipation of the SM. The CKM is also found to over-predict the SGS viscosity. Compared with these two models, the SMSM and the CSM have performed well in predicting both the averaged and the instantaneous flow-fields of the compressible jet. And they are localized models which are computationally efficient and easy for coding. Therefore, the SMSM and the CSM are recommended for the LES of the compressible Jet.
