Unsteady flow field in a vaned centrifugal pump diffuser

This paper describes experimental and computational work to examine the unsteady flow field in the vaned diffuser a medium specific speed pump. The aim of this project is to verify a commercialy available Navier-Stokes program with a k-epsilon turbulence model and to improve our understanding of the complex unsteady three-dimensional flow field associated with the interaction between a pump impeller and its vaned diffuser. The paper provides the results of experiments carried out using Laser Doppler Anemometry (LDA), in which time-resolved details of the unsteady flow field in a vaned diffuser of a medium specific speed pump have been obtained as a function of the local position of the pump impeller blades. The static pressures were also measured at the hub and shroud side of the diffuser. The measurement results have been analysed to elucidate some interesting flow features observed in this typical pump diffuser. These include unsteady recirculation of the flow from the diffuser into the impeller at partload and flow separation in the diffuser channel. The unsteady flow simulation of a two dimensional diffuser showed the capabilities and the limits of a Navier Stokes program with k-epsilon turbulence model. The comparisons of the simulation results with experimental data identify that this simple computational model with a time periodic inlet profile is able to show important flow phenomena. In terms of the flow field and pressure rise there is no substantial difference between the predictions of a steady simulation and the time-average of an unsteady simulation.