Unsteady Numerical Simulation Of Low-specific-speed Pump With Complex Impeller

As the one of main flowparts in low-specific-speed centrifugal pump, impeller is totranform the mechanical energy of original motive into the pressure and kinetic energy of liquid,so the structure of the centrifugal impeller has a crucial role on flow condition and performanceof pump. Based on Reynolds-averaged Navier-Stokes equations and the RNG k-ε turbulencemodel, the whole flow field in low-specific-speed centrifugal pump with four-blade, eight-blade and twelve–blade impeller was simulated respectively in this thesis. And the experimentalinvestigation was also carried out on three low-specific-speed centrifugal pumps. The maincontents were as follows:The whole flow field in low-specific-speed centrifugal pump with four-blade, eight-bladeand twelve–blade impeller were completed by three-dimensional modeling software Pro/e, thevelocity and pressure distribution inside pump flow field were simulated by using FLUENT atthree different time. In addition,the pressure fluctuations were analyzed by setting upmonitoring points near the wall of volute and tongue.Finally,the pump external characteristicsreached by numerical prediction and experimental results were compared.After analysis,conclusions are as follows:(1) From the velocity analysis, it can be seen that the channel between the two long bladesis relatively wide and the fluid cannot be clamped well for ordinary impeller without splitterblades. As the result, fluid coming from the thick boundary layer on blade pressure side can notbe successfully discharged. So there exists a large area of low speed recirculation zone betweentwo blades inside four blades impeller, which is improved inside the other two impellers withsplitter blades. To some extent splitter blade can improve velocity distribution in the channel ofimpeller;(2) As can be seen in the static pressure analysis, static pressure distribution inside twelveblades impeller is more uniform and static pressure coefficient is significantly greater than fourblades impeller blades in the same radius, the same change rules can been also seen insidevolute chamber and the exit.All is indicating that splitter blades can not only improve thepressure distribution inside the pump, but also increase the pressure at same location;(3) From pressure fluctuation analysis, numerical results show that the complex impeller can significantly improve the pressure fluctuation inside volute chamber. Compared withordinary impeller, it is worth noting that frequency components generated by the compleximpeller is more complex. In addition to fundamental frequency and its harmonic, pressurefluctuation generated by the long blades play the dominant role in low frequency region forcomplex impeller;(4) The experimental results show the higher head is obtained by the pump with twelveblades. The pump shaft power becomes larger with the increase of the number of blades, whichwill affect pump efficiency to a certain extent.