Effect of inlet elbow on rotation stall in waterjet propulsion pump

To study the influence of an elbow inlet on the rotating stall characteristics of a waterjet propulsion pump (WJPP), a three-dimensional internal flow field in a WJPP under a straight-pipe inlet and elbow inlet is numerically simulated. By comparing the hydraulic performance of WJPP under the two inlet conditions, the internal relationship between the inlet mode and the flow pattern in the pump is clarified. Based on unsteady pressure fluctuation characteristics and wavelet analysis, the influence of the inlet mode on the rotating stall is revealed, and the stall transient propagation characteristics under critical stall conditions are analyzed. The disturbance effects of the inlet channel geometry disappear under low flow rate conditions, the main disturbance is induced by the high-speed countercurrent, and the flow pattern under the elbow inlet is better than that under the straight-pipe inlet. Under the straight-pipe inlet, the single-stall nucleus in the WJPP temporarily experiences a low-frequency and high-amplitude disturbance, which subsequently transforms into a mode of multi-stall nuclei with high-frequency circumferential disturbance. Under the elbow inlet, the rotating stall always maintains a mode of high-amplitude and low-frequency disturbance, which represents the transient characteristics of a single stall core propagating in the circumferential direction inside the channel. The results of this study have a reference value for structural design optimization in a WJPP.