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Concentrated separation vortex induced by non-uniform suction flow and its role in performance breakdown of a water-jet pump

Many water-jet pumps have a suction velocity profile, which is non-uniform and unfavorable for the pump performance. This article applies the numerical method to investigate the generation mechanism of performance breakdown in a water-jet pump under non-uniform suction flow. The mechanism dictating flow details in the impeller, including the inlet velocity, flow angle, and boundary layer separation, is systematically studied at the design point. Observations show that the nature of non-uniform inflow is a circumferential distortion upstream of the impeller shroud, which is proved to be a stationary stall cell associated with a velocity deficit near the top sector. Meanwhile, a detailed analysis allows the identification of flow separation and vortex in the impeller. The circumferential distortion gives rise to a high incidence, the occurrence of suction surface separation, and the consequent formation of a concentrated separation vortex near the blade shroud. Furthermore, particular attentions are devoted to the pressure distribution and blade loading in the shroud section. Deviating from the suction surface, the concentrated separation vortex produces a considerable pressure rise on the suction surface and generates a remarkable drop in blade loading. Consequently, the concentrated separation vortex associated with circumferential distortion is a major reason for the head breakdown of a water-jet pump.