Effects Of Blade Deflector Structure On The Cavitation And Fluid-solid Coupling Characteristics Of An Axial Flow Pump

Cavitation is a phenomenon that is not conducive to the normal operation of the pump,which affects the transport capacity of the pump slightly and destroys the flow passage components of the pump seriously.Therefore,the study of cavitation control in pump is of great significance.In this paper,the cavitation flow of TZX700 axial flow pump is studied firstly.On this basis,the anti-cavitation modification is carried out,and the cavitation control structure named blade deflector is proposed.Then the cavitation flow numerical calculation,single-phase fluid-solid coupling calculation and prestressed modal analysis of the axial flow pump before and after modification are carried out.The influence of deflector structure on the cavitation characteristics,structural characteristics and vibration characteristics of the pump is explored,which provides a certain reference value for the anti-cavitation optimization design of the axial flow pump.The main research contents are as follows:1)The cavitation distribution and development in the prototype pump were analyzed.It was found that the cavitation in the prototype pump was initially generated near the inlet edge of the blade tip region.With the decrease of net positive suction head available(NPSHa),it gradually developed to the outlet edge and the blade root.The mechanism of cavitation leading to the decrease of the energy characteristics of the impeller is analyzed.It is found that the cavitation gathered near the blade tip hinders the mainstream of the impeller.When the cavitation is serious,excessive cavitation will destroy the continuity and stability of the mainstream flow,resulting in the change of the velocity distribution in the impeller channel,which affects the energy conversion in the impeller and causes the decrease of the pump head.2)In order to determine the best layout position of blade deflector,five different layout schemes of deflector are proposed,and the external characteristics and cavitation characteristics of different schemes are compared and analyzed.It is found that the layout scheme near the inlet has better cavitation resistance.The internal cavitation flow of the pump before and after modification was analyzed.It was found that the cavitation volume fraction of the main cavitation area on the pump blade decreased after the layout of blade deflector,and the cavitation area shifted towards the outlet edge.The anti-cavitation performance of blade deflector under eccentric condition was analyzed,and it was found that deflector still had certain cavitation inhibition at 1.1Qd and 0.9Qd.3)The mechanism of the anti-cavitation performance of deflector structure is explored.It is found that the absolute pressure in the main producing area of the bubble over pump blade increases after deflector is arranged,and the extension length of the low pressure area in the main producing area of cavitation decreases.The two changes of the pressure field inhibit the development of airfoil cavitation and weaken the strength of airfoil cavitation,and the diversion effect of the deflector itself has a certain inhibitory effect on the development of airfoil cavitation.4)Fluid-solid coupling calculation and pre-stress modal analysis were carried out on the axial flow pump impeller before and after modification under different cavitation allowances.It was found that the maximum deformation of the pump impeller was reduced and the area of the high deformation area was also reduced after the layout of the deflector,indicating that blade deflector improved the structural strength of the pump impeller.It is also found that the development of cavitation in the pump has little effect on the inherent vibration frequency of the pump,and blade deflector has little effect on the inherent vibration frequency of the pump,but it has a significant effect on the vibration mode of the pump.