In order to improve the hydraulic performance of existing super low-specific-speed multistage centrifugal pumps, based on ANSYS CFX, the whole flow field of a series of multistage centrifugal pumps is simulated. The energy conversion efficiency and hydraulic loss in the impeller, casing and diffuser are analyzed by defining the head and efficiency for each of them. As a result, the primary factor affecting the performance of the multistage centrifugal pump is identified to be the matching between impeller and diffuser, and the secondary factor is the flow loss in the impeller. It is proposed that the throat area of diffuser should be calculated by making use half magnitude of the absolute velocity at the impeller outlet, the designed diffuser is optimized step by step and the vortex in the impeller is eliminated by adjusting the impeller blade profile. The fluid velocity in the impeller and optimal diffuser varies uniformly and slowly, reducing the flow loss significantly. The optimized pump is manufactured, tested and compared with the original one. It is shown that the head and efficiency are significantly improved by 8.1 m and 3.2%, respectively, meeting the requirements in the national pump standard. The method in which the simulated results are compared with the measurements and then the differences between them are analyzed can provide a reference for hydraulic performance optimization of a super low-specific-speed multistage centrifugal pump.
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