(98x) Reduction of Turbophoresis By Polymer Additives

Turbophoresis is the migration and accumulation of particles towards the wall in wall-bounded turbulent flow. Its importance appears in many applications; for example, industrial processes related to coatings, paints, or inks, where metallic powders are added to polymeric solutions to obtain desired chromatic or thermo-chromatic features. In this study, we qualitatively and quantitatively observe the effects of drag reducing polymer additives on turbophoresis of inertial particles in turbulent channel flow. The analysis is based on data from a direct numerical simulation (DNS) of a polymeric turbulent channel flow modeled with FENE-P and laden with particles with different inertia, i.e. Stokes numbers. Data show that polymer additives decrease the turbophoretic drift. Reduction in turbophoresis is associated to an increase in particle transport through the channel. We establish that turbophoresis is reduced because of the smaller derivative of wall-normal fluid velocity fluctuations that are typical of drag reducing flows. Hence a reduction of turbophoresis should be a common feature of all drag reducing flows, e.g. with fibers or bubbles and MHD.