Formation of damage pits by cavitation in a polymer solution

Abstract

Cavitation damage is a serious problem in the operation of modern high-speed hydrodynamic machinery. To suppress cavitation inception, polymers have been added to the water¹; however, the effect of polymer addition on cavitation damage^2–5 has not yet been studied in detail, and there has been no literature on the pitting mechanism in polymer solutions. We show here that the forms and processes of formation of cavitation damage pits in specimens in a polymer solution are totally different from those in water. Oblique and pot-shaped damage pits are formed on a flat, smooth surface of a specimen in a polymer solution. If the specimen has artificial pits such as small conical or cylindrical holes, the parts with small radius of curvature are apt to be damaged, although the smooth surfaces are not. These phenomena are specific to polymer solutions (non-newtonian fluids), and cannot be seen in newtonian fluids such as water.