Near-wall lubricating layer in drag-reduced flows of rigid polymers

We experimentally investigate the drag-reduced channel flow of an inelastic, shear-thinning rigid polymer solution. Particle image velocimetry and shear-viscosity measurements are used to obtain instantaneous distributions of the shear viscosity within the turbulent domain. We elucidate that drag reduction for rigid polymers is primarily driven by a thin lubricating layer that consists of low-viscosity fluid near the channel wall.