Energy dissipation characteristics of reversible mixed-flow pump at pump and turbine modes based on entropy production theory

This study investigates the energy loss characteristics and pressure pulsation patterns of a reversible mixed-flow pump (RMFP) at both pump and turbine modes through numerical analysis. The results demonstrate that: in pump mode, the volute domain exhibits the highest entropy production rate at 80% of the design flow rate, with significant energy loss occurring at the impeller shroud region (Span = 0.8) due to flow separation. Under turbine mode, the impeller domain dominates entropy production, and the hub region (Span = 0.2) shows maximum entropy generation rate at low water head, indicating reduced energy conversion efficiency. Pressure pulsation analysis reveals that the dominant frequency at the point near the volute tongue is 6× rotational frequency in both modes. However, the pulsation amplitude in pump mode is primarily governed by the impeller tongue interaction, whereas in the turbine mode it stems mainly from high-potential-energy fluid impact in the inflow passage. The study elucidates the key loss mechanisms of RMFP under different operational modes, providing the theoretical foundations for optimal design.