Research On The Influence Of Tip Clearance On The Stable Operation Of Vertical Submersible Axial Flow Pump

Vertical submersible axial flow pumps are widely used in fields such as drainage and irrigation,dock propulsion and water conservancy projects due to their large flow and low head delivery characteristics.As the main working part,the impeller is related to the performance of the entire axial flow pump.Considering the needs of installation and operation,a certain gap clearance should be left at the top of the blade rim to avoid friction.This thesis takes the 350ZQ-125 high specific speed vertical submersible axial flow pump as the research object,and compares the influence of different tip clearances on the internal and external characteristics,static performance,pressure fluctuation and axial force of the axial flow pump through numerical calculation methods,and explores the clearance The effect of size on the safe and stable operation of axial flow pumps.The research content and main conclusions are as follows:(1)Using Bladegen combined with Turbogrid software to establish the three-dimensional hydraulic model and grid model of the full channel under different blade tip clearances,the blade tip clearance values are 0 mm(0%D),0.5 mm(0.18%D),1.0 mm(0.36%D),2.0mm(0.72%D),3.0 mm(1.07%D)and 5.0 mm(1.79%D),the RNG turbulence model is used to calculate the established numerical model.(2)Based on constant numerical calculations,the influence of the blade tip clearance on the external characteristics of the axial flow pump,the pressure and load distribution on the blade surface,the pressure and velocity distribution at the blade tip clearance,and the vortex pressure and velocity distribution in the impeller under different working conditions are explored.The results show that the blade tip clearance has a significant impact on the performance of the axial flow pump.Under the design flow condition of 1.0 Qd,the head decreases by 1.28 m and the efficiency decreases by 12% when the clearance value δ changes from 0.5 to 5 mm.The change of the blade tip clearance will lead to the increase of the blade face load and pressure difference,and have an impact on the pressure distribution on the blade surface,the flow velocity in the center,and the swirl pressure and velocity distribution in the impeller.The pressure and velocity of the vortex increase first and then decrease with the increase of the blade tip clearance.(3)The influence of the blade tip clearance on the stress and deformation of the impeller and guide vane is studied by using the fluid-solid coupling calculation method.The results show that the increase of tip clearance can significantly reduce the stress on the blade.The main deformation of the impeller occurs near the rim of the water inlet,while the response of the guide vane to the change of the clearance is small.In the design of axial flow pumps,the blade tip clearance is an important parameter,and factors such as axial deformation and radial deformation need to be considered comprehensively.(4)Using the unsteady calculation method,the pressure fluctuation characteristics in the axial flow pump and the change of the axial force on the impeller under different blade tip clearances are studied.The results show that the internal pressure pulsation of the axial flow pump is mainly caused by static and dynamic interference.When considering the blade tip clearance,the pressure pulsation is affected by the clearance leakage,and the low-frequency pulsation is mainly in the water inlet horn flow channel and guide vane flow channel.The pressure value of the impeller inlet section increases with the increase of the gap value,and the pressure value of the impeller outlet section and guide vane outlet section decreases with the increase of the gap value;the pulsation amplitude decreases with the increase of the gap value.