REYNOLDS STRESS AND VORTICAL STRUCTURE IN A UNIFORMLY SHEARED TURBULENCE

The spatial structure of the Reynolds shear stress in a uniform shear turbulence is investigated by the direct numerical simulation of Navier-Stokes equations and by the rapid distortion analysis. It is observed that many thin vortex tubes of various shapes develop from a random initial velocity field. The Reynolds shear stress also has tube-like structure and takes especially large values between pairs of counter rotating vortices aligned in the spanwise direction as was revealed before by conditional averaging (Adrian & Moin 1988). The turbulent kinetic energy increases exponentially in time as has been observed in laboratory experiments. The rapid distortion analysis demonstrates that the tube-like structure can be created only through the linear interaction of the turbulent velocity with the mean strain, leaving the velocity field be Gaussian. The organized structure does not necessarily imply non-Gaussianity of the velocity field.