Numerical Study On Cavitation Flow Characteristics Of Centrifugal Pumps Under Low Flow Conditions

Cavitation is a common phenomenon in the normal operation of water pumps.Cavitation erosion,vibration and noise are caused by cavitation flow restrict the development of water pump industry in China severely.Therefore,it is of great significance to study the cavitation problem in order to find an effective way to predict and suppress the cavitation flow for the pump to maintain high efficiency and stable operation.In this paper,a medium specific speed centrifugal pump is taken as the research object and the internal flow condition of the centrifugal pump under cavitation,non-cavitation and sand-bearing conditions is numerically calculated by combining test and numerical simulation.Considering the influence of centrifugal pump rotation and its geometric structure on cavitation flow,the traditional ZGB mass transport cavitation model is improved in this paper.Meanwhile,the turbulent viscous coefficient of RNG k-εturbulence model in two-phase flow region is revised to overcome the defect of overestimation of turbulent viscous coefficient of RNG k-ε turbulence model.The improved cavitation model and turbulence model are used to simulate the centrifugal pump under 0.8Qd flow condition.The numerical results of the external characteristics of the centrifugal pump agree with the experimental results well,which verifies the accurateness of the calculation model.The modified RNG k-ε turbulence model and the improved ZGB mass transport cavitation model were used to simulate the unsteady flow of centrifugal pump under 0.8Qd flow rate with non-cavitation and three different cavitation number(NPSAHa=1.59m,1.21m and 0.99m)conditions.The streamline distribution and cavitation shape in impeller of centrifugal pump under different cavitation numbers were analyzed.Combining with the pressure fluctuation characteristics,illustrated the evolution process and shedding mechanism of the cavitation.At the same time,compared the overall change trend and law of movement of the internal flow of centrifugal pump under cavitation and sand bearing conditions,and analyzed the influence of sand particles on the cavitation flow.