Reynolds Stress and Vortical Structure in a Uniformly Sheared Turbulence

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The spatial structure of the Reynolds shear stress ita a uniform shear turbulence isinvestigated by Late direct numerical simulation of Navier-Stokes equations and by tlaerapid distortion analysis. It is observed that many thin vortex tubes of various shapesdevelop from a random initial velocity field. Tlte Reyx-tolds slaear stress also has tube-like structure and takes especially large values betweexe pairs of counter rotating vor-tices aligned in the spanwise direction as was revealed before by conditional averaging(Adrian & Moin 1988). The turbulent kinetic energy increases exponentially in time ashas been observed in laboratory experiments. The rapid distortion analysisdemonstrates that the tube-like structure can be created only through the linear in-teraction of the turbulent velocity with the mean strain, leaving the velocity field beGaussian. The organized structure does not necessarily imply non-Gaussianity of thevelocity field.[Reyno1ds stress, uniform shear, turbulence, numerical simulation, vortex, ex- l[ ponential growthl
1992-12-15