On the scale locality and vortex stretching in homogeneous shear turbulence

Abstract

The interscale transfer of kinetic energy and Reynolds stress in homogeneous shear turbulence (HST) is numerically investigated using three-dimensional bandpass filtering technique. The flow fields of a statistically steady HST are obtained using direct numerical simulation at three Reynolds numbers 2000, 5000, and 12 500 based on box depth. Visualizations of typical flow structures of bandpass filtered fields show that the small-scale structures are nearly isotropic, whereas the large-scale ones show the preferential alignment with the direction of mean shear. Quantitative results of both kinetic energy and Reynolds stress fluxes between two specific scales show the existence of scale locality. In specific, the eddies of a length scale L mostly transfer their energy or Reynolds stress to eddies of size 0.3L to 0.4L, which seems to be independent in the limit of the high Reynolds number. Furthermore, through the analysis on the vortex stretching, it is shown that the small-scale structures of scale Lω are stretched mostly by straining structures of size about 2 Lω, while large-scale structures are stretched mostly by mean shear. Finally, the evaluation of alignment between vortical structures and strain rate shows that small-scale structures are more likely to align with the strain structures of five times their size, and large-scale ones are mainly align with the mean shear strain. These findings can help enhance our comprehension of the interscale transfer and scale interaction of vortical structures in turbulence.