Impact of Subgrid-Scale Models on Jet Turbulence and Noise

Introduction V ISBAL and Rizzetta1 and Visbal et al.2 have recently performed large-eddy simulation (LES) calculations of turbulent channel flow and compressible isotropic turbulence decay without using any explicit subgrid-scale (SGS) model. In those simulations, spatial filtering was treated as an implicit SGS model. They also showed that use of an SGS model in those simulations did not produce results superior to those obtained without employing an SGS model. Bogey and Bailly3 also performed LES calculations for jet flows by using spatial filtering only. Moreover, they brought up the issue of the effects of the eddy–viscosity-based Smagorinsky SGS model on jet noise in yet another recent study.4,5 They showed that the high-frequency portion of the noise spectra was significantly suppressed by the eddy–viscosity. It is well understood that in turbulent flows the energy cascade is associated with a mean flux of energy that is directed from large scales toward small scales. The large scales contain the major part of the turbulent kinetic energy, and they continuously feed the turbulent kinetic energy via the cascade to the smallest eddies where it is dissipated. Because the grid resolution is too coarse to resolve all of the relevant length scales in an LES, the pile-up of energy at high wave numbers can be eliminated through the use of a spatial filter. Hence, the spatial filter can be thought of as an effective SGS model in an LES. In this study, we perform two jet simulations to study the impact of the SGS model on jet turbulence and far-field noise. The first simulation does not employ any explicit SGS model, but treats the spatial filter as an implicit SGS model. In the second simulation, we employ a localized version of the dynamic Smagorinsky model (DSM) (see Ref. 6) and keep all test case parameters the same as those in the first simulation. We examine the differences between the two simulations to quantify the effect of the SGS model on the near-field jet turbulence and the far-field noise. Although this study is similar to those done by Bogey and Bailly,4,5 our work additionally does a comparison of the two LES results with experimental jet noise spectra with the hope

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