Effect of Polymer Additives on Jet Cavitation

Abstract

Cavitation in a fluid jet discharged under the surface of a similar fluid was studied using water and dilute solutions of poly(ethylene oxide), a drag-reducing polymer. The addition of a few parts-per-million of poly(ethylene oxide) to the fluid reduced the cavitation-inception index to about one-half the pure-water value. Upstream turbulence increased the cavitation inception index with water but had little effect on cavitation inception with polymer solutions. The viscosity, air content, nuclei number, and tensile strength of the polymer fluid was found to be essentially the same as water, and the surface tension lowered; hence an explanation of the reduced cavitation-inception index observed in polymer solutions must be sought in the changed fluid dynamics of the polymer jet. Photographs of polymer jets discharging in air are presented to aid in the explanation.