Investigation of Hydraulic Design for High Performance Multi-Stage Pump Using CFD

We investigated the hydraulic design and flow field in a multi-stage pump to achieve high efficiency and low cavitation performance using computational fluid dynamics (CFD) and experimental approaches. The subject of the investigation is a four-stage centrifugal pump, which consists of a suction bend, impellers, stators, and a discharge volute. In designing a high performance multi-stage pump, it is important to investigate the interaction of flows between the stator and impeller, which were also investigated individually for minimizing hydraulic loss. The flow field in the suction bend, therefore, was simulated first using conventional CFD based on the Reynolds-Averaged Navier-Stokes (RANS) equations, and the calculated result of the flow field at the outlet of the suction bend was used to design the impeller inlet shape at the design-flow rate. To obtain a high-performance impeller shape, the effect of the meridional configuration of the impeller on hydraulic loss was examined using a parameter design based on conventional CFD results. The meridional shape was composed of several design parameters such as inlet, outlet diameter and so on, and a few parameters, which contribute to reducing hydraulic loss significantly, were extracted using the parameter design. Therefore, we obtained a highly efficient impeller shape by adjusting those important parameters. Finally, to evaluate and confirm the interaction of the flows between the stators and impeller, a numerical calculation of the four-stage pump was carried out using advanced large eddy simulation (LES). As a result, we obtained the predicted flow field in the four-stage pump. There was no significant flow separation at the inlet of each impeller and it was confirmed that the blade design was appropriate. The hydraulic performance of the four-stage pump was also confirmed using a model pump test. The inception of cavitation was observed and the cavitation coefficient estimated using experimental results was in good agreement with the CFD prediction. As a result of this development including the investigation described above, the hydraulic shape of a highly efficient and high-cavitation performing four-stage pump was obtained.