Unsteady flow characteristics in low-specific-speed centrifugal pump with complex impeller

To investigate the unsteady flow characteristics caused by interaction between the impeller and volute in the low-specific-speed centrifugal pump,the unsteady flow field of a centrifugal pump with four-long and eight-short blades was simulated based on sliding mesh and RNG k-e turbulence model.The simulation results of velocity and static pressure show highly asymmetric in space as well as highly unsteady in time.The velocities on sections Ⅳ and Ⅷ of volute have the same trend,and the circumferential velocity decreases along the radial direction of volute.The change of radial velocity magnitude on section Ⅳ is less than that on section Ⅷ because section Ⅳ is away from the tongue and is less influenced.The flow near the volute is the most complex and the radial negative velocity appears on section Ⅷ.The rotor-stator coupling is the main reason for pressure fluctuation,whose frequency is dominated by impeller rotating frequency,and the dominant frequency is blade passing frequency.The amplitude of fluctuation pressure along the volute fluctuates from sectionⅠ to section Ⅷ,and its average value declines gradually until section Ⅷ reaches a minimumvalue.Compared with the steady calculation,the effective head calculated by unsteady calculation is closer to experimental value at design point,indicating that the unsteady calculations can predict the pump head accurately.