Mitigation of Unsteady Excitation in a Large Vertical Centrifugal Pump Under Flow Instability Via Novel Diffuser Configurations

Abstract Hydraulic excitation under flow instability threatens the operational safety of large vertical centrifugal pumps (LVCP), which are crucial in long-distance water transfer systems. This study uses delayed detached eddy simulation (DDES) to examine the unsteady excitation behavior of LVCP with two novel radial vaned diffuser designs, diffuser B and diffuser C. Diffuser B integrates large and small hydrofoil vanes, while diffuser C features a gradually varying hydrofoil layout. Simulation results reveal diffuser B postpones the head drop compared to diffuser A, while diffuser C exhibits the highest and most consistent head under part-load conditions. Diffuser C also reduces pressure pulsation intensity by up to 53.54% and low-frequency pulsations by 57.87%, especially at low flow rates. While diffuser B shows limited improvement in excitation forces, diffuser C not only markedly reduces the pulsation intensity of the excitation force but also mitigates the imbalance of radial excitation force in the circumferential direction, particularly under deep stall conditions with a maximum reduction of ΔFR to 80 N. Internal flow analysis indicates that the nonuniform pressure rise from the inlet to the outlet of diffuser A is the primary cause of pressure pulsation and excessive radial excitation force. The incremental hydrofoil vane assembly in diffuser C significantly reduces velocity variations across different blade spans and enhances the uniformity of pressure distribution. Additionally, diffuser C effectively suppresses large-scale vortex rotational propagation in the flow channel. These improvements collectively contribute to better control of unsteady hydraulic excitation in LVCP under unstable operating conditions.