Experimental study of the effects of viscosity and viscoelasticity on a line vortex cavitation

Abstract

This paper investigates the influence of viscosity and viscoelasticity on the structure of the flow in a line vortex in view of understanding their effects on cavitation inception. Experiments were conducted in a vortex chamber where the fluid injection speed and the liquid properties can be easily controlled. Measurements of the velocities, pressures, and thus the cavitation number were conducted using a PIV system, pressure gauges, and Pitot tubes. Experiments were performed using water, different dilute concentrations of polymer (POLYOX WSR 301) solutions, and solutions with different concentrations of corn syrup for a large range of Reynolds numbers. The measurements and observations showed that cavitation inception at the vortex center was delayed when polymer and corn syrup solutions are used as compared to the experiments in water. However, contrary to reported observations with tip vortices, here the large scale vortex was found to rotate faster in the polymer and corn syrup solutions. This did not match with our observations of cavitation inception delay in the case of polymers and the conventional thinking about the relationship between pressures and velocities in a vortex line. This may be due to the observations that the velocity fluctuations and the turbulent kinetic energy in the viscous core region increased significantly in the polymer and corn syrup solutions and could question the validity of a pressure computation based on a single vortex.