Transient Fluctuations in Hydraulic Performance and Energy Dissipation in a Tubular-Flow Pump with Highly Twisted Blades

Periodic fluctuations in pump head are a common unsteady phenomenon in tubular pumps; however, their underlying energy dissipation mechanism remains insufficiently understood. This study conducted transient numerical simulations on a two-blade tubular-flow pump with highly twisted blades operating at the design flow condition. Using entropy production theory, the research quantitatively examined Rotor–Stator Interaction (RSI), vortex development, and hydraulic loss characteristics. The findings reveal that turbulent entropy production is the primary contributor to total energy dissipation, while entropy generated by wall friction is minimal. Although the impeller experiences the greatest absolute energy loss, the fluctuations in entropy production within the guide vane are significantly larger. This indicates that the energy loss represented by the entropy production in the guide vane primarily drives the periodic head fluctuations of the pump. High entropy production is concentrated near both the leading and trailing edges of the guide vane, exhibiting a trough-shaped radial distribution influenced by the leading-edge hub vortex and tip leakage vortex. Additionally, the transient changes in entropy production under RSI are governed by the periodic formation and strengthening of the guide vane passage vortex, along with the shedding and breakdown of the wake vortex. Velocity analysis shows that the circumferential movement of the impeller wake continuously modifies the instantaneous inflow conditions at the guide vane’s leading edge, causing periodic changes in the incidence angle that enhance the passage vortex while weakening the wake vortex. This study provides deep insights into the operational stability of pumps and pumping stations in water transfer projects.