Temporal behavior of strong shear layers in high Reynolds number turbulence

High resolution direct numerical simulation (DNS) of isotropic turbulence with the Taylor micro-scale Reynolds number $R_\lambda=O(10^3)$ on $4096^3$ grid points was used to study the temporal behavior of strong shear layers in high Reynolds number turbulence. A time span of $10\tau_\eta=2.55\lambda/u'$ was simulated and analyzed, where $\tau_\eta$ is the Kolmogorov time-scale, $\lambda$ is the Taylor micro-scale and $u'$ is the $rms$ value of the velocity fluctuations. Detailed visualization showed excellent correspondence between regions with high enstrophy values and the existence of strong shear layers. Reasonably close-packed elongated strong vortices were found to exist in layer-like regions with thickness of the order of $\lambda$. A quantitative analysis of the DNS data showed that in these strong shear layers, strong vortices interact with the neighboring vortices and move drastically at a speed of the order of $u'$, maintaining an effectively constant distance between each other. The average size of these peak vortices also remains quasi-time-independent. The strong shear layers at the interfacial region remain sharp during the time evolution. These shear layers are significant intermittent structures of high Reynolds number turbulence.