Research On The Effect Of Blade Outlet Cutting Mode On Low Specific Speed Centrifugal Pump Fluid Induced Noise

As a kind of mechanical equipment that converts mechanical energy into fluid energy,pumps are usually accompanied by strong vibration and noise during operation,which will not only have a great impact on the life and performance of mechanical equipment,but also spread to human ears through the air,causing great harm to human body.Noise pollution will seriously affect human physical and mental health,therefore,reduce the noise of pump has become a hot research topic.In this paper,the single-stage single-suction centrifugal pump is taken as the target object,on the basis of not changing the parameters of the shroud and hub of the impeller,the influence law of the impeller after cutting on the noise of the centrifugal pump is studied by cutting the blade outlet in different ways.Based on the RNG k-?turbulence model and the acoustic boundary element/finite element（BEM/FEM）method,the full flow field and full sound field of the centrifugal pump are calculated respectively.After the transient calculation of the flow field of the centrifugal pump is completed,the dipole sound source is obtained.Then,based on the finite element calculation results of the centrifugal pump,the acoustic vibration coupling is adopted to study the change law of the internal and external sound field of centrifugal pump after blade cutting.The research results can provide a certain basis for reducing the noise of centrifugal pump.The main contents of this paper are as follows:1.Influence of blade outlet edge forward cutting on hydraulic noise of centrifugal pump.By cutting the outlet edge of the impeller blade forward,the blade after cutting makes the fluid flow into the volute passage more smoothly.The results show that:The internal pressure energy of the centrifugal pump is mostly focused on the blade passing frequency and its low frequency harmonic frequency,and the pressure pulsation distribution directly affects the noise of the centrifugal pump,and the pressure pulsation and the noise of internal and external sound fields are concentrated in the low frequency band,reaching the maximum at the blade passing frequency.The blade outlet cutting can make the pressure change in each section inside the volute uniform,the sound pressure level inside and outside the centrifugal pump and the sound power at the blade passing frequency will gradually decrease with the increase of the cutting distance at the blade outlet.Considering the energy performance and flow field noise of centrifugal pump,when the impeller blade outlet cutting amount is 1.21%,that is,the clearance rate between impeller blade and tongue is 8.57%,the comprehensive performance of centrifugal pump is the best.2.The influence of V-shaped cutting of blade outlet edge on the hydraulic noise of centrifugal pump.The V-shaped cutting width of blade outlet and the best choice of volute tongue can be adjusted by V-shaped cutting of impeller blade outlet,so as to improve the flow state of fluid in impeller outlet and volute channel.The results show that:the V-shaped cutting at the impeller blade outlet can reduce the change of turbulent kinetic energy at the impeller outlet and weaken the vortex intensity in the back cavity of the pump,so as to improve the flow state and streamline distribution in the cavity of the centrifugal pump.Different V-shaped cutting shape of blade outlet can reduce the pressure fluctuation of volute tongue,and the fluctuation intensity of volute tongue pressure fluctuation can well reflect the sound pressure level in centrifugal pump,and is closely related to the sound pressure level in centrifugal pump.The V-shaped cutting width of blade outlet is a/b₂=33.33%,it can not only ensure the minimum reduction of head and efficiency of centrifugal pump,but also ensure the best noise reduction effect of sound pressure level in centrifugal pump.Different cutting width has different effects on the pump body excited by fluid,the external acoustic field noise of centrifugal pump is mainly affected by the internal flow field and pump body.3.Influence of blade outlet oblique cutting on pressure pulsation and hydraulic noise in front and rear cavities of centrifugal pump.The outlet diameter of the shroud and hub of the impeller is kept unchanged by chamfering the outlet edge of the impeller blade,to improve the pressure change of the centrifugal pump cavity,so as to reduce the noise inside and outside the centrifugal pump.But the blade outlet angle is not easy to be too large,which will affect the performance of centrifugal pump.The results show that:The change of blade outlet angle has obvious change on pressure fluctuation inside the front and rear cavities of the pump and sound field noise.When the blade outlet oblique angle increases,the head and efficiency loss of the centrifugal pump is within the acceptable range,the pressure pulsation of the front and rear cavities,the pressure pulsation at the impeller passage and the noise sound pressure level of the internal and external sound field are all decreasing,and the reduction degree of the pressure pulsation and the noise sound pressure level of the internal and external sound field is gradually obvious with the increase of the oblique cutting angle of the blade outlet.