Drag Reduction in Liquid-Liquid Friction

We study the effect of the addition of long flexible polymers in stratified flows. A two-layer stratification is used, in which the lower layer is brought into motion and drives a two-dimensional turbulent flow in the upper layer through viscous friction. Upon polymer addition in either of the two layers the kinetic energy in the upper layer is reduced by roughly one-half: The polymer reduces the liquid-liquid friction that drives the flow in the upper layer. This drag reduction can be attributed to a change in the nonsteady viscous boundary layer. The main characteristics of the quasi-two-dimensional turbulence that results in the upper layer are found to remain unaffected by the addition of the polymer.