Experimental and Numerical Study of Unsteady Flow in a Diffuser Pump at Off-Design Conditions

Abstract

An experimental and numerical study was developed for the unsteady phenomena at off-design conditions of a diffuser pump. Unsteady pressure measurements were made downstream of the impeller, and the pressure fluctuations were analyzed using the ensemble averaging technique as well as the statistical and chaotic time series analysis. The unsteady flow was classified into five ranges as a result of the statistical and chaotic time series analysis. And a two-dimensional vortex method was employed to investigate the unsteady flow structure due to the interaction between impeller and diffuser vanes in a diffuser pump at various off-design conditions. The numerical results of unsteady flow at a partial discharge range (approximately 83% of the rated flow rate) show an asymmetrical separation bubble near the pressure surface of the impeller vane. The intermittence of the separation bubble may be the main factor to cause the unstable characteristics of the test diffuser pump. The calculated unsteady flow at the lower partial discharge range (50% of the rated flow rate) presents a rotating stall in the impeller passage as well as in the diffuser passage, which can be main cause of unstable characteristics there.