The effect of polymer additives which lower the friction resistance on flow in smoothly contracting and expanding channels

Abstract

Vortical formations near the wall and their subsequent disintegration are sources of turbulization of the flow [1, 2]. Their intensity at smooth walls depends on the magnitude and the sign of the longitudinal pressure gradient [1]. With considerable values of a negative pressure gradient, vortices do not develop. In a number of publications, for example [3], note is taken of the special importance of vortices of the transition layer in the phenomenon of the lowering of the friction resistance by polymer additives. In this work, experimental investigations were made of flows with negative and positive pressure gradients. Data are obtained which attest to the fact that the flow of weak solutions of polymers with negative pressure gradients does not differ from the flow of Newtonian liquids, while, with positive gradients, the effect of polymer additives manifests itself fully.