Experimental and mechanistic study on the stability improvement of axial flow pump equipped with end wall injection

To explore effective flow control methods that can enhance the operational stability of axial flow pumps, an experimental and numerical study was conducted on a specific axial flow pump equipped with end wall injection. The influence of injector number on the pump performance was analyzed through experiments. Combined with pressure fluctuation testing, the mechanism by which end wall injection improves pump stability was revealed. The results indicate that end wall injection can substantially improve the operational stability of the axial flow pump without reducing its efficiency under the design point. As the number of injectors increases, the stall margin of the axial flow pump rises accordingly. When the number of injectors is four, the axial pump achieves maximum efficiency under the design conditions. At this time, using a 5.6% injection flow rate can increase the pump efficiency and stall margin by 1.83% and 48.2%, respectively. Pressure pulsation testing and unsteady numerical simulations identify that forward spillage of tip leakage flow and passage vortex induce large-scale blockage in blade passages. These phenomena generate rotating stall cells covering half the annulus, ultimately causing abrupt head drop during operation. The high-velocity jet greatly suppresses the tip leakage flow and reduces tip blockage, while completely eliminating rotating stall phenomena. Meanwhile, end wall injection enhances energy conversion capacity under low-flow conditions and expands the stable operating range. The research confirms that end wall injection can serve as a robust flow control strategy for stability improvement of axial flow pumps.