Effect Of Water Injection On Cavitation Performance Of Axial Flow Pump

The instability of cavitation will seriously affect the performance of hydraulic machinery in applications such as ship propulsion,underwater vehicles and hydropower stations,and cause vibration,noise,and even mechanical damage to the hydraulic machinery.For this reason,reducing and controlling cavitation in the operation of hydraulic machinery is the focus and difficulty of cavitation research in recent decades.In order to study the flow control of cavitation,this paper takes the hydrofoil and the axial flow pump as the research objects,and proposes a method to effectively control the internal cavitation of hydraulic machinery.Based on the numerical simulation,the effect of water injection on the cavitation flow control and pump performance is studied.Numerical simulation of cavitation flow is a complex flow calculation that integrates turbulent flow and multiphase flow.The homogeneous flow model ignores the compressibility of the flow when calculating the cavitation flow,which makes the turbulence model unable to accurately predict the turbulent viscosity at the near-wall region.In order to predict the multi-scale cavitation flow more accurately,considering the compressibility of the cavitation flow,a comparative analysis of turbulence models with different correction methods is carried out.The cavitation flow phenomenon studied by using the filter-based density correction turbulence model and the Zwart-Gerber-Belamri cavitation model is in good agreement with the experimental results of cavitation flow around the hydrofoil.Arranging jet holes or water injection on the suction surface of the hydrofoil can effectively reduce the development length of cavity.In the absence of water injection,the hydrodynamic performance of the hydrofoil is improved,but the volume of the cavity increases,and cavitation also occurs in the cavity of hydrofoil.The water injection reduces the volume of the cavity,reduces the shedding frequency,and reduces thickness of velocity boundary layer,which enhances the anti-reverse pressure gradient capability of the flow.The water injection control technology is applied to the axial flow pump,and the research of water injection control cavitation is carried out in axial flow pump.Numerical results show that: when the water injection is arranged in the cavity attachment area,the cavity volume is significantly reduced,the net positive suction head available of the axial flow pump increases by 2.9%,the pump efficiency increases by 0.6%,but the head of the axial flow pump decreases by 4.6%.However,when the water injection is arranged outside cavity attachment area,the water injection flow fluctuates greatly,the flow is disturbed obviously near the jet holes,but the jet still has a good effect on cavitation control.The water injection is arranged on the surface of the blade of the axial flow pump,the reverse pressure gradient of the blade surface is reduced,and the flow in the axial flow pump is smoother,which can effectively inhibit the development of cavitation in the axial flow pump.However,the water injection will cause the drop and fluctuation of the operating performance in the axial flow pump,which is mainly reflected on the drop and fluctuation of the head of the axial flow pump.On the whole,arranging water injection in the cavitation attachment area of the axial flow pump impeller is an effective measure to reduce cavitation in the axial flow pump.