Investigation of energy performance and unsteady flow characteristics of a multi-stage centrifugal pump under various seal wear conditions for renewable energy pumping systems

A novel multi-stage centrifugal pump with floating impellers, employed in renewable energy pumping systems, flexibly adjusts the number of stages to meet various underground water levels. The floating impeller, combined with sealing gaskets, effectively reduces the axial force, enhancing the pump's lifespan and stability. However, once seal wear occurs, the axial oscillation amplitude of the floating impeller increases, severely affecting the operation of the pumping system. Using computational fluid dynamics simulations with a coupled dynamic mesh and multiple reference frames, the impact of different levels of seal wear is analyzed. Repeated experiments confirm the accuracy of simulations. As the impeller oscillation amplitude increases, pump performance significantly deteriorates. The total leakage increases by up to 114 %, with reductions in head coefficient and efficiency reaching 8.8 % and 4.3 %, respectively. Entropy production within the pump intensifies, and the velocity and pressure distribution change noticeably. The increase in impeller oscillation amplitude leads to a maximum increase of 457 % in pressure fluctuations within the impeller, with increases exceeding 200 % in both the side chamber and return guide vane. The impeller oscillation frequency, as the fundamental frequency of pressure fluctuations, sees an amplitude increase of up to 594 % within flow channels. This study provides valuable insights for stabilizing the performance and reliability of multi-stage centrifugal pumps.