Velocity-vorticity correlations and the four-layer regime in turbulent channel flow of generalized Newtonian fluids

Y The data of Arosemena et al. (2021), consisting of turbulent channel flow simulations of generalized Newtonian (GN) fluids, are considered to study the effects of shear-dependent rheology on the nonzero velocity-vorticity correlations and the mean dynamics. In the near-wall region and compared to Newtonian channel flow, the velocity-vorticity products contributing to the turbulent inertia term decrease/increase with shear-thinning/thickening fluid behaviour suggesting that with e.g. shear thinning rheology, the sublayer streaks are more stable, the near-wall vortical motions are dampened and there is a narrower range of turbulent length scales. The mean momentum balance analysis, on the other hand, revealed that the four-layer structure first recognized by Wei et al. (2005a) remains for all GN fluids and that the shear-dependent rheology only seems to influence the location of the layers. For instance, with shear-thinning behaviour, layers II and III are thicker and there is an increase in the importance of the viscous forces in these intermediate layers. The influence of shear-thinning/ thickening fluid behaviour on the extent of the layers II and III is found remarkably similar to an increase/decrease of the Reynolds number for Newtonian channel flow. These findings suggest that the shear-dependent rheology should also be taken into account for proper scaling of the intermediate layers. A potential length scale factor is proposed and its suitability is tested. (C) 2021 The Author(s). Published by Elsevier Masson SAS.