Influence of shear-thinning fluid on vortex formation in pulsatile, turbulent flow

Vortex formation in shear-thinning fluids is an important research topic due to their ubiquity in biological and engineering contexts. Vortices formed in shear-thinning fluids have been shown to possess lower circulation, propagate a smaller distance, and have reduced local strain rates compared to those formed in Newtonian fluids (Palacios-Morales and Zenit, 2013). The presence of vortical structures affects the overall macro characteristics of the flow such as fluid mixing and drag. In the present work, we have investigated these structures using time-resolved PIV measurements in a pulsatile flow loop experiment, comparing both a xanthan gum shear-thinning fluid and a Newtonian fluid. The field of view is downstream a stenosis model designed to create vortical structures when the flow loop is operated in a pulsatile manner to produce unsteady and very unsteady flows. The parameter space includes transitional to turbulent mean Reynolds numbers and non-negligible Strouhal numbers. Steady cases at the respective mean Reynolds numbers are tested for comparison. Flow field analysis has been carried out to elucidate the differences between the two fluids where it is predicted that the viscoelastic properties of the xanthan gum affects the flow physics and could reduce mixing.