LES of Internal Flows in a Mixed-Flow Pump With Performance Instability

This paper describes large eddy simulation (LES) of the internal flows of a high-specific-speed mixed-flow pump at low flow-rate ratios over which measured head-flow characteristics exhibits weak instability. In order to deal with a moving boundary interface in the flow field, a form of the finite-element method in which overset grids are applied from multiple dynamic frames of reference has been developed. The method is implemented as a parallel program by applying a domain-decomposition programming model. The predicted pump heads reproduce the instability and agree quantitatively well with their measured equivalents although the predicted stall takes place at somewhat lower flow-rate ratio than in the measurements. The phase-averaged distributions of the meridional- and tangential-velocity components at the impeller’s inlet and exit cross-sections were also compared with those measured by a Laser-Doppler velocimetry (LDV). Reasonably good agreements have been obtained between the computed and measured profiles. The developed LES program thus seems to be a promising design tool for a high specific-speed mixed-flow pump particularly for off-design evaluations.