Study on power losses and pressure fluctuations of diffuser mixed flow pump as turbine on different power generation speeds based on energy power models

Variable speed regulation represents an effective means to ensure the efficient operation of the diffuser mixed flow pump as turbine (DMFPAT). This paper employed computational fluid dynamics-based energy power models and high-frequency water pressure fluctuation tests to investigate the power losses and pressure fluctuations of DMFPAT under different power generation speeds. Analysis of power losses reveals that internal power losses in DMFPAT predominantly originate from the turbulent dissipation power (PEPD′) in the entropy production and the turbulent kinetic energy production power (PEBL3) in the energy balance equation, indicating that fully developed turbulence significantly contributes to substantial power losses in DMFPAT. A strong correlation exists between power generation speed and power losses, and decreasing rotational speed results in gradual reduction of power losses in DMFPAT. Additionally, a comprehensive analysis of the pressure fluctuation signals of DMFPAT under variable speed mode was conducted, revealing that the main frequency at each monitoring point is the rotational frequency and its harmonics. As speed decreases, the pressure fluctuation amplitude diminishes. The research presented demonstrates that adjusting the speed not only markedly reduces power losses but also eliminates adverse pressure fluctuations, thereby providing a theoretical basis for the efficient, stable and safe operation of DMFPAT.