SINOPSIS

The objective is to investigate flow topology and related Reynolds-number scaling in the eigenframe of the strain-rate tensor for wall-bounded turbulent flows. The databases used in the current study are from direct numerical simulations (DNS) of fully developed channel flow up to friction Reynolds number Re_τ ~ 1500, and a spatially developing, zero-pressure-gradient turbulent boundary layer up to Re_θ ~ 4300 (Re_τ ~ 1400). It is found that for all cases considered, the averaged flow patterns in the local strain-rate eigenframe appear universal: large scale motions are separated by a shear layer with a pair of vortices. Based on Kolmogorov (η, u_η), Taylor (l_t) and integral length scales, Reynolds-number scalings of the averaged flow patterns, including the thickness and strength of the shear layer, the distance between the two vortical regions, and the velocity distribution along the most compressing and stretching directions are considered. It is found that the Taylor scaling of the profiles for the thickness of the shear layer seems more suitable than the Kolmogorov scaling, and the integral scaling collapses well away from the shear layer, which confirms that those patterns represent large scales. Generally speaking, the scaling profiles based on the Kolmogorov length and velocity collapse well near the origin, but the Taylor scaling seems best suited in a broader region.