Numerical Study On Cavitation Performance Of Axial Flow Pump With Different Blade Mounting Angles

Cavitation is a harmful phenomenon for hydraulic machinery.The generation and development of cavitation in hydraulic machinery will change the velocity distribution in the channel,resulting in the decrease of energy characteristics of hydraulic machinery.The development of cavitation will destroy the flow passage parts to a certain extent,and even cause the vibration and noise of hydraulic units.Therefore,it is of great significance to study the internal cavitation of hydraulic machinery.In this paper,the internal cavitation phenomenon of the axial flow pump is studied and analyzed by numerical calculation method.The cavitation law of the axial flow pump under different blade mounting angles is analyzed and summarized,which provides certain reference value for scientific research and engineering practice.Taking TZX-700 horizontal axial flow pump as the research object,SST model is used for turbulence model and Rayleigh-Plesset model for cavitation model.The numerical results are compared with experimental results to verify the correctness of numerical calculation.The accuracy of numerical calculation is further guaranteed by grid independence analysis and Y+of the main computational domain of the axial flow pump.Through numerical calculation of a blade mounting angle under different inlet pressure,it is found that the cavitation in the axial flow pump first occurs at the top of the blade near the impeller blade inlet.With the further decrease of the inlet pressure,the cavitation develops to the blade outlet and hub.When the inlet pressure is 0.1 MPa,the suction surface of the blade of the axial flow pump has cavitated.When the inlet pressure further drops to 0.07 MPa,the head of the axial flow pump decreases to 3%,that is,the critical cavitation allowance of the axial flow pump is 7.79m at the blade mounting angle.On the basis of other parameters unchanged,the cavitation performance of the axial flow pump was numerically studied by changing the blade mounting angle(+4°?+2°?0°?-2°).It is found that the critical cavitation allowance decreases with the decrease of blade mounting angle.The NPSHcr values of critical cavitation allowance are 7.79m?6.77m,6.45m and 5.94m,respectively.The cavitation performance is improved.In order to further analyze the cavitation performance of axial flow pumps under different flow conditions,the cavitation performance of axial flow pumps under low flow conditions(0.9Q)was studied.It was found that under the same inlet pressure,compared with the design flow conditions,the cavitation area on the blade surface was further expanded under low flow conditions,and the cavitation area developed to the blade outlet and hub.In order to study the transient cavitation flow field of an axial flow pump,the unsteady values of the cavitation flow field of an axial flow pump under different flow conditions are calculated.The results show that the cavitation flow field of an axial flow pump under the design conditions changes with time to a certain extent.The pressure fluctuation at the inlet and outlet of impeller shows periodicity in the time domain diagram,and the main frequency of pressure fluctuation in the frequency domain diagram is the rotation frequency of the axial flow pump.