Effects of Mean Shear on Homogeneous Turbulence. Turbulence Statistics and Turbulence Models.

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  • 一様乱流におけるせん断の影響　統計的性質と乱流モデル
  • イチヨウ ランリュウ ニ オケル センダン ノ エイキョウ トウケイテキ セイ

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The effects of mean shear enforced on decaying isotropic turbulence have been investigated by numerical experiments with the direct numerical simulation (DNS) of Navier-Stokes equations. In flows rapidly distorted from isotropy, it is important to elucidate the behavior of turbulent quantities, in particular, the pressure-strain correlations contributing to the origin of the anisotropic state. The pressure-strain term in the Reynolds stress equations becomes positive only in the spanwise velocity fluctuations, and hence turbulence energy is extracted from components in both streamwise and shear directions. The redistribution process as well as the anisotropic behavior of turbulence statistics are accurately evaluated with a linear analysis based on the rapid distortion theory. Furthermore, from the assessment of turbulence models for pressure-strain correlations using the present DNS data, it is found that none of the existing models represent the energy sink from the shear direction except for a model using the Langevin equation, and the destruction of the Reynolds shear stress is described rather well using a classical linear model.

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