Evolution of a hairpin vortex in a shear-thinning fluid governed by a power-law model

Abstract

The effect of a shear-thinning fluid governed by a power-law model on the evolution of a hairpin vortex in a wall-bounded flow was studied by means of direct numerical simulation. With a fixed Reynolds number and hairpin vortex strength, the effect of shear-thinning on vortex evolution could be isolated. The primary observation is that very early in time shear-thinning has the effect of reducing the production of vortex kinetic energy and dramatically increasing viscous dissipation. This leads to a delay in the transition of the flow to a turbulent state. Three-dimensional flow visualizations reveal that the increased dissipation is associated with an instability in which the hairpin vortex is broken down into small-scale structures. It is suggested that the finite amplitude of the hairpin creates a lowering of viscosity near the hairpin vortex core which leads to this instability.