Stall recovery mechanism for an axial flow waterjet pump based on end wall injection

To solve stall-induced flow instability and performance degradation in axial flow waterjet pumps, an active stall recovery method integrating stall warning and end wall injection is proposed. Experimental tests were conducted to evaluate the recovery performance of end wall injection under stall-locked and dynamic stall modes, coupled with full-annulus unsteady numerical simulations to clarify the underlying mechanism. The results demonstrate that the proposed method can restore pump stability within 3 s, with the stabilized pump head increasing by over 25% compared to the stalled state. Specifically, the stall warning criteria exert negligible influence on the recovery efficacy under the stall-locked mode. The critical minimum injection flow rate for stall recovery is 6% of the design flow rate, and the optimal injection flow rate is 8%. In dynamic stall mode, earlier stall warning yields superior recovery performance, and the stall warning should be triggered before the pump enters deep stall. Mechanistic analysis reveals that forward spillage of the tip leakage vortex (TLV) interacts with the passage vortex (PV), inducing large-scale tip blockage that evolves into a rotating stall cell. End wall injection mitigates TLV–PV interactions, driving disordered vortex clusters to evolve into helically twisted TLVs. This enhances the tip through-flow capacity and blade tip loading, thereby enabling stall recovery. This study provides a reliable active control strategy for stall recovery in axial flow waterjet pumps, offering technical support for the safe operation of hydraulic engineering equipment.