Computational cavitating viscous liquid flows in a pump as turbine and Reynolds number effects

Abstract

Cavitating flows of viscous oils in an experimental centrifugal pump with low specific speed are modeled and simulated by using the time-averaged Navier–Stokes equations and standard k - ɛ turbulence model as well as full cavitation model based on the computational fluid dynamics method, when the pump operates in the reverse direction as turbine to generate power. The cavitation characteristics are identified at part-load, best efficiency and over-load points and five viscosities. Effects of viscosity on net positive suction head required are clarified. Net positive suction head required correction factor and conversion factor curves are obtained and correlated to impeller Reynolds number. The flow and cavitation models are validated with the existing experimental results and empirical correlations. Pressure and helix angle profiles at the draft tube entrance, cavity shape, swirling flow pattern in the draft tube, and the pressure coefficient distribution over the blade surfaces are presented. The presented results can be useful for design, selection, performance prediction, and impeller redesign of a pump as turbine.