Indirect Probing of the Strain-Rotation Balance in Non-Newtonian Turbulence with Inertial Particles

It is commonly thought that small amounts of polymer additives alter the strain-rotation balance in turbulent flows. However, as for experimental evaluation of this hypothesis one needs to resolve the velocity gradients in turbulent flows, quantitative evidence for this statement is mostly lacking. Velocity gradients are notoriusly challenging to measure in most experiments, so here we take an alternate, indirect approach to answer the question on how polymers affect turbulent flows. By using the well-known preferential concentration effect of inertial particles and the energy flux balance model for polymer turbulence, we can probe concentration effects on the strain-rotation balance. We do so by using a classical von-Kàrmàn water flow with high-molecular-weight polymer additives of varying concentration and weakly inertial particles. We compute the pair correlation function and show that particle clustering and hence the strain-rotation balance is monotonically altered with increasing polymer concentration.