MECHANISM OF REDUCTION OF FRICTION BY ADDITION OF POLYMERS TO FLOWS.

A mechanism for the reduction of frictional drag by polymeric additives (Toms effect) is suggested. The macromolecules are assumed to uncoil in the jets existing in the turbulent wall flow, orienting themselves along the extension direction and producing a mobile lattice. This hinders ejections into and from the mainstream, and decreases their intensity and frequency. The longitudinal viscosity, which increases sharply in extensional flow when these polymeric molecules are present, is due both to the molecular properties of the polymers and to transverse turbulent transport. The basic equations of an improved semiempirical theory of wall turbulences in dilute polymer solutions are given.