Abstract
In homogeneous shear flow, turbulence exhibits anisotropic properties affecting all scales of motion at finite Reynolds numbers. Upon releasing the mean shear, the anisotropy characterizing the velocity field decays over a large eddy turnover time. The decay of the anisotropy of the vorticity field, however involves a range of time-scales, from the short (Kolmogorov) time scale, up to the large eddy turnover time.
Highlights
We investigate by direct numerical simulation (DNS) the decay of the Reynolds stress tensor and the correlations of the velocity gradient tensor in homogeneous shear-released turbulent flows that are initially maintained at statistically steady states at moderate Reynolds numbers
To evaluate the quality of the statistics obtained from the Nc configurations, we compared some lower-order moments of the homogeneous shear flow obtained by averaging over the entire time of the run, and from the Nc selected configurations, for each of the two Reynolds numbers investigated
We have investigated the return to isotropy of a homogeneous turbulent flow, initially in the presence of a large-scale uniform shear and in statistical steady state, after the imposed shear is released
Summary
Whereas the paradigm of homogeneous, isotropic turbulence (HIT) provides a convenient frame to analyze flows at high Reynolds numbers [1,2,3,4,5,6], HIT can be realized only in numerical simulations. For a homogeneous flow in the absence of any forcing, the return of the Reynolds stress tensor towards the isotropic form is driven by the viscous dissipation and by the pressure-rate-ofstrain correlation, psi j [33], where si j ≡ (∂iu j + ∂ jui )/2 is the rate of strain tensor of the turbulent fluctuation and ∂iu j denotes throughout the partial derivative ∂u j/∂xi Understanding these different terms is of fundamental interest; it has important potential implications in engineering [8]. To this end, we investigate by direct numerical simulation (DNS) the decay of the Reynolds stress tensor and the correlations of the velocity gradient tensor in homogeneous shear-released turbulent flows that are initially maintained at statistically steady states at moderate Reynolds numbers.
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