An inclined groove and its optimization design method for improving the energy performance at the saddle zone of axial flow pumps

Energy conservation and emission reduction have become a global focus issue with the development of technology. Axial flow pumps, as an energy conversion device, play an important role in pumped storage and water source transportation. However, axial flow pumps experience severe energy loss under low flowrates, affecting the energy performance and stability of the hydraulic system. This paper proposed an inclined groove flow control method to improve the performance at the saddle zone. The performance was investigated experimentally and numerically with and without grooves. The result shows that inclined grooves significantly enhance the energy characteristics at the saddle zone, with a 56.5 % increase in head at 0.4Q_des and a 40.17 % increase at 0.5Q_des. The local low-pressure zone upstream and downstream of the inclined groove creates a reverse flow inside the groove, mixing with the mainstream in the inlet pipe and weakening the circumferential angular momentum. The improved inflow condition mitigates flow separation within the pump and suppresses the propagation of tip blockage vortex. Entropy production analysis reveals that inclined grooves effectively suppress energy losses in the inlet pipe. Moreover, a dimensionless number NOG is proposed for the design of the inclined grooves. It is found that the ideal NOG range is between 0.014 and 0.022, which optimizes energy performance in the saddle zone while minimizing negative effects under the design condition.