Effect of the number of blades on diffuser unsteady loss of centrifugal pump

Abstract

In recent years, an unshrouded impeller is being developed for rocket turbopumps to reduce production costs and disk friction losses. However, the internal flow structure in a diffuser influenced by an impeller has not been clarified yet. In this study, we focused on the investigation of unsteady flow in turbopumps with unshrouded impellers and vaned diffusers by experiments and CFD. Furthermore, we investigated the effect of changing the number of blades of the impeller and diffuser on the unsteady losses in the diffuser. First, we measured the static pressure at the shroud side in the impeller and the velocity at the diffuser inlet and outlet. Second, we confirmed the accuracy of the CFD by comparing CFD results with experimental results. Third, we investigated unsteady losses in diffusers by CFD. We could confirm increased entropy at the suction surface and shroud side because of the tip leakage and the vortex. Finally, we changed the number of impeller blades or diffuser blades. In conclusion, the loss region at the suction surface and the high-pressure region at pressure surface in the unshrouded impeller were mixed and caused unsteady losses through the diffuser. And diffuser efficiency decreased because channel width in diffuser became narrower by the number of diffuser blades increasing.

Optimal Design of High-Speed Partial Flow Pumps using Orthogonal Tests and Numerical Simulations

“…When the liquid in a single flow channel connects to the diffuser along the tangential direction, it is discharged [9,10]. Ueda et al [11] investigated the impact of impeller blade number on pump performance through simulation and experimentation. They found that as the number of blades increases, the flow velocity fluctuations in the pump decrease in frequency, and the flow path becomes smaller, leading to an increase in losses within the pump.…”