Structure of turbulence at high shear rate

The structure of homogeneous turbulence subject to high shear rate has been investigated by using three-dimensional, time-dependent numerical simulations of the Navier–Stokes equations. The instantaneous velocity fields reveal that a high shear rate produces structures in homogeneous turbulence similar to the ‘streaks’ that are present in the sublayer of wall-bounded turbulent shear flows. Statistical quantities such as the Reynolds stresses are compared with those in the sublayer of a turbulent channel flow at a comparable shear rate made dimensionless by turbulent kinetic energy and its dissipation rate. This study indicates that high shear rate alone is sufficient for generation of the streaky structures, and that the presence of a solid boundary is not necessary. Evolution of the statistical correlations is examined to determine the effect of high shear rate on the development of anisotropy in turbulence. It is shown that the streamwise fluctuating motions are enhanced so profoundly that a highly anisotropic turbulence state with a ‘one-component’ velocity field and ‘two-component’ vorticity field develops asymptotically as total shear increases. Because of high shear rate, rapid distortion theory predicts remarkably well the anisotropic behaviour of the structural quantities.