Numerical and experimental investigation of the flow in a centrifugal pump stage

In the first part of this paper, a steady state numerical simulation of the first stage of a multistage centrifugal pump, consisting of an impeller, a diffuser and a return channel, is performed by the commercial software Ansys-CFX. The obtained simulation results are compared with experiments that are designed and conducted by Laser Doppler Velocimetry (LDV) in the diffuser region for the same part load point. The experiments are done in a test facility which has been especially prepared for optical flow measurements. To reduce the numerical effort for this calculation a stage interface between rotating and stationary frames and a periodic boundary condition (only one blade of each blade row is simulated) is used for this calculation. For the stage interface, the flow behind the impeller is averaged circumferentially to be the inflow conditions of the diffuser blades. The experimental investigations support the simulation results. In the second part of this contribution the transient flow in this pump stage, which has an impeller with seven blades, a radial diffuser with ten vanes and a return channel with also ten separate vanes, has been simulated transient with the same software. Because of the unfavorable ratio of blade numbers a complete meshing of all flow channels was necessary. In consequence the cumulative amount of grid nodes reached a number of nearly 6 million nodes for this calculation. As a result of the numerical investigation of the time dependent flow accomplished for this part, the influence of the rotating impeller on the flow in the stationary parts of the pump is presented in detail. For this operation point all flow parameters are shown as a function of time and are discussed with respect to the position of the impeller relative to the stator vanes.