Co-adjustable guide vane and diffuser vane to improve the energy generation potential of an axial-flow pump as turbine

Operating an axial-flow pump as turbine (APAT) with a high head can be a cost-effective solution for energy recovery applications. However, axial-flow pumps are characterized by a low head, which makes it difficult for an APAT to achieve high efficiency. In this study, computational fluid dynamics–based numerical simulations were performed using steady and unsteady Reynolds-averaged Navier-Stocks equations and a shear stress transport reattachment modification turbulence model to investigate how the energy performance and operating range of an APAT can be improved under low-head conditions. The experiment was conducted to evaluate the accuracy and reliability of the numerical results. Adjusting the diffuser vane (DV) and guide vane (GV) were identified as candidate solutions. The adjusting mechanism was designed and presented in both 2D drawings and 3D model. Further simulations were performed to evaluate the effect of the clearances at the hub and shroud of the GV and DV. While the clearances at the GV had no adverse effect on the energy performance, clearances at the DV greatly reduced the energy performance because of the formation and growth of leakage vortex flows. Adjusting the DV improved the energy performance more than adjusting the GV. A co-adjustable GV and DV is a comprehensive solution that was found to increase the efficiency of the APAT by 40.15 % under low-head conditions and weaken vibration and noise by suppressing the separation flow in the GV domain.