The Reynolds Average Navier-Stokes/Large Eddy Simulation (RANS/LES) turbulence model has significant advantages in solving separated flows and providing high-precision transient flow field information. This paper employs DDES turbulence model to conduct numerical research on the bulb tubular pump model, specifically focusing on the stall condition and the design condition. The three-dimensional vortex structures have been visualized with the Omega vortex identification method, revealing the formation of large-scale stall vortex structures in the impeller at low flow rates and their impact on flow parameter fluctuations and low-frequency pressure pulsation characteristics. The mismatch between the flow angles of the impeller and diffuser exacerbates the stall in the diffuser, and the transverse pressure gradient at the trailing edge of the impeller leads to separated flow near the hub. The periodic evolution of low-pressure vortex structures explains the low-frequency characteristics of pressure fluctuations to a certain extent. Quantitative analysis of energy loss is conducted using total pressure and entropy generation methods, and it is found that turbulent entropy generation is the main source of loss at low flow rates, closely related to vortex structure. This study also identifies that stall phenomenon is mainly caused by large-scale flow separation resulting from the small flow angle of the impeller at low flow rates. These findings of this paper can provide reference for the optimization design and operation stability of pumps.
Sun et al. (Sun,) studied this question.