Cavitation Control Mechanism Of Low Specific Speed Centrifugal Pump Based On Bionic Jet Principle

With the rapid development of social economy,the state has put forward strict energy consumption standards for all walks of life,also including the pump industry.However,the occurrence of cavitation in centrifugal pump seriously restricts the improvement of centrifugal pump performance.At the same time,when cavitation occurs in the centrifugal pump,the shock wave produced by cavitation bubble collapse will erode the surface of flow passage components,which will reduce the service life of the pump system and increase the economic loss.From the biological research of sharks,it is found that the jet formed by the breathing process of sharks in the water can effectively increase the stability and the hydrodynamic characteristics of sharks in the swimming process.Inspired by this kind of jet structure,apply it to the cavitation control of centrifugal pump.In this paper,a low specific speed centrifugal pump with a specific speed of 32 is selected.The numerical simulation method is used to analyze the cavitation development process in the impeller and the influence of bionic jet structure on the cavitation bubble evolution process in the centrifugal pump.In the research process,the modified SST k-?turbulence model is obtained by redefining the viscosity coefficient?_t in the SST k-?turbulence model,which solves the problem of over prediction of vapor viscosity in the original turbulence model.Choose Kubota cavitation model in numerical calculation of cavitation.And the feasibility of the numerical simulation scheme is verified by the test method.In this paper,the development process of cavitation in low specific speed centrifugal pump and the cavitation control scheme based on bionics principle are studied,and the following conclusions are obtained:(1)The maximum error of numerical calculation is 4.86%,which is within the allowable error range.In the process of numerical simulation,the selection of turbulence model,cavitation model,boundary conditions and mesh scheme are all reasonable.This numerical simulation scheme can be used for subsequent research.(2)Through the analysis of cavitation flow field in the impeller of centrifugal pump,it is found that with the decrease of NPSH_a,the cavitation phenomenon in the impeller becomes more and more obvious.The dynamic and static interference between the impeller and volute results in the asymmetric distribution of cavitation bubbles in the impeller of centrifugal pump.The surface load of the impeller is related to the inlet pressure and cavitation bubble state of the impeller.When the pump inlet pressure drops,the blade surface load also drops.At the same time,the existence of cavitation bubble will affect the work ability of the blade,cause the change of the surface load of the blade.It is found that the pressure fluctuation in the impeller presents the change characteristics of the main frequency,the pressure pulsation in the impeller takes the blade frequency as the main frequency,which is closely related to the cavitation state.(3)Through the study of the influence of different bionic jet structure on the cavitation performance of low specific speed centrifugal pump.It is found that the bionic jet structure can effectively inhibit the development of cavitation bubbles in the impeller.Under the same head,the radial width of 3 mm and the axial width of 10 mm,the NPSH_a is 42%smaller than the original model.Under the condition of head fracture,the head can be increased by 33.7%.The jet changes the size of cavitation volume fraction,but does not change its trend of change.The radial width of 3 mm and the axial width of 10 mm,the cavitation volume fraction can be reduced by 43.6%.The jet effectively inhibits the expansion of the inner low pressure area,so that the area of the low pressure area is significantly reduced,and the influence of the axial length of the jet hole on the pressure distribution in the impeller is less than the radial length.When cavitation occurs in the impeller,the vibration of the cavitation will change the vortex structure and turbulent kinetic energy in the impeller,which will increase the loss of the impeller and decrease the pump head.The occurrence of cavitation in impeller will lead to the change of vortex structure and turbulent kinetic energy in impeller,and the jet action will change the distribution structure of flow field in impeller,and affect the turbulent kinetic energy and vortex structure,thus affecting the occurrence and development of cavitation in impeller.The bionic jet structure does not change the frequency-domain change rule and the main frequency amplitude change rule,but changes the main frequency amplitude,the pressure pulsation of P1,P2,P3 and P4 is mainly affected by cavitation flow in impeller,and the pressure pulsation of P5 and P6is mainly affected by the dynamic and static interference between impeller and volute.(4)Through the analysis of the influence of bionic jet structure on the performance of centrifugal pump,it is found that the bionic jet structure has different influence on the performance of centrifugal pump under different flow rates.Under the condition of small flow rate and rated flow rate,the head and efficiency of centrifugal pump decrease and the performance of pump becomes worse;under the condition of large flow rate,the jet field helps to optimize the flow field structure and improve the head and efficiency of pump.For the optimal cavitation control scheme,the bionic jet has little effect on the performance of the pump,which can be put into engineering practice.