Experimental Study and Theoretical Analysis of the Rotating Stall in a Vaneless Diffuser of Radial Flow Pump

This paper reports an experimental and theoretical study of rotating stall in a vaneless diffuser which is coupled with a radial impeller. The experiments were conducted at 22 flow rates for two rotating speed: 1200rpm and 1800rpm. The measurements have consisted of: i/ unsteady pressure measurements delivered by two microphones flush mounted on the vaneless diffuser, ii/ 9 steady pressure taps mounted in one radial line on the diffuser to measure the pressure recovery in the vaneless diffuser. The stability of each stall mode was also studied by a 2D linear analysis; and the theoretical prediction was compared to experimental observations. The capabilities and limits of such an approach to predict the development of rotating stall have been evaluated. A non-dimensional analysis of the pressure losses at outlet was conducted to evaluate the effect of the instability development on the performance of the diffuser. It has shown that the arising of rotating stall has a positive effect on the diffuser performance.