Numerical study on the internal flow characteristics of an axial-flow pump under stall conditions

Abstract

When an axial-flow pump works in low flow rate conditions, rotating stall phenomena will probably occur, and the pump will enter hydraulic unsteady conditions. The rotating stall can lead to violent vibration, noise, turbulent flow, and a sharp drop in efficiency. This affects the safety and stability of the pump unit. To study the rotating stall flow characteristics of an axial-flow pump, the steady and unsteady internal flow field in a large vertical axial-flow pump was investigated using 3D computational fluid dynamic (CFD) technology. Numerical calculations were carried out using the Reynolds-averaged Navier–Stokes (RANS) solver and Menter's shear stress transport (SST) k-ω turbulence model. Steady flow characteristics including streamline, velocity vector, pressure and turbulent kinetic energy are presented and analyzed. Unsteady flow characteristics are described using post-processing signals for pressure monitoring points in the time and frequency domains. Using Q-criterion, the locations and evolution rules of the core region of the vortex structure in guide vanes under deep stall conditions were investigated. The reliability of the numerical simulation results was verified using the experimental prototype pressure fluctuation test. In this way, typical flow structure and pressure fluctuation characteristics in an axial-flow pump were analyzed, with contrastive analysis in design condition and stall conditions. Finally, the mechanism of low-frequency pressure fluctuation in a pump unit under the stall condition was revealed.