| In recent years,the demand for centrifugal pumps in the country has grown rapidly and the production capacity of centrifugal pumps has increased tremendously.The market has increasingly higher requirements for the performance of centrifugal pumps,and cavitation is an important issue that cannot be avoided.O nce serious cavitation occurs during the operation of the centrifugal pump,the accumulated cavitation will block the flow channel and have a serious impact on the hydraulic performance of the centrifugal pump.The collapse of the cavitation will cause cavitation on the wall of the impeller and cause the impeller to fail.The vibration and noise brought by the collapse process will affect the stable operation of the entire system.Therefore,studying the cavitation mechanism and exploring the cavitation control strategy has important application value.Cavitation first appears near the leading edge of the inlet blade of the centrifugal pump impeller,and the roughness of the leading edge of the blade ha s an important influence on the flow of fluid.In this paper,the numerical simulation method is used to study the effects of different rough zone arrangement schemes on cavitation characteristics,external characteristics,pressure,turbulent kinetic energy,and pressure fluctuation of a low specific speed centrifugal pump.The main contents and innovations of this paper are as follows :(1)Summarize the basic theory of cavitation and commonly used cavitation research methods;sum up the current research status of the airfoil,centrifugal pump,and axial flow pump cavitation control.Cavitation control of the centrifugal pump is mainly divided into the following three ways: one is to appropriately increase the inlet pressure to reduce the occurrence of cavitation;two is to optimize the basic geometric parameters that affect cavitation performance;the third is to control the cavitation flow by changing some structural features based on the structure of the prototype pump impeller;The related research on surface roughness and roughness zone is given.(2)The basic flow control equations solved by numerical methods and several commonly used turbulence models and cavitation models are introduced.The centrifugal pump test platform was described in detail,and the centrifugal pump hydraulic performance test and cavitation performance test were completed.Numerical calculations of the external characteristics and cavitation flow of the centrifugal pump are carried out.The head curve and efficiency curve obtained by the centrifugal pump simulation are in goo d agreement with the experimental values.The maximum error of the head obtained by the numerical calculation is 4.8%,and the maximum error of the efficiency is 4.7%,which are all within the allowable range.The reliability of the numerical simulation method is verified.(3)Through numerical simulation of cavitation of two different cross-section shapes of semi-circular arc and rectangle with three heights of 0.3 mm,0.5 mm,and0.9 mm,the results show that the two kinds of cross-section shapes of rough zone schemes can suppress cavitation under reasonable height.This is because most of the cavitation mainly occurs in the leading edge of the suction surface of the blade.Th e arrangement of the rough zone reduces the fluid velocity near the front end of the rough belt,increases the pressure in this area by losing part of the velocity,and reduces the scope of cavitation.Moreover,the rough zone can improve the turbulent kinetic energy distribution in the impeller,and make the higher turbulent kinetic energy distribution area closer to the inlet direction,so that the transition from laminar flow to turbulent flow can be realized in advance,which is conducive to the suppression of cavitation.From the cavitation characteristics,the semicircular arc rough zone is better than the rectangular rough zone.When the cavitation numberσ=0.84,the reduction of cavitation volume by the semicircular arc is smaller than that by rectangular rough belt,but the loss of velocity and head is also relatively small,while the reduction of cavitation volume by rectangular rough zone is larger,but the loss of velocity and head is also larger;when the cavitation number is reduced to σ=0.24,overall,the volume of cavitation is reduced by the semicircular rough zone better than that of the rectangular rough zone,and the semi-circular rough belt with the height of rough belt of 0.5mm has the best inhibition effect on cavitation volume,while the rectangular cross-section rough belt with the height of rough belt of 0.9mm increases the cavitation volume.(4)Through the cavitation numerical simulation study on the three different rough zone heights of 0.3mm,0.5mm,and 0.9mm under the cross-sectional shape of the semicircular arc and rectangular rough zone,it is found that when the cavitation number is σ=0.84,The height of the rough zone is increased from 0.3mm to 0.9mm,and the suppression of the cavitation volume in the impeller becomes more eff ective;the cavitation number is reduced to σ=0.24,and the semi-circular arc rough zone increases from the height of the rough zone from 0.3mm to 0.5mm,the suppression effect increases slightly,and the height of the rough zone increases from 0.5mm to0.9mm,and the suppression becomes worse.For the rectangular rough belt,as the height of the rough belt increases,the suppression effect gradually becomes worse,so that when the height of the rough belt is 0.9mm,the increase of the cavity volume in the impeller is aggravated.This is because when the degree of cavitation development is weak,the increase in height is beneficial to weaken the fluid velocity and increase the pressure.However,cavitation develops in-depth.As the height of the semi-circular rough zone increases,it has a weaker effect on the fluid flow.As the height of the rectangular rough zone increases,the transition from laminar flow to turbulent flow is realized later.This is not true.Conducive to the development of inhibition.(5)The numerical simulation of cavitation is carried out for the schemes of 0.3mm,0.5 mm,and 3 mm,9 mm,and 15 mm with the semicircular rough zone.The results show that when the cavitation number is σ=0.84,the inhibition effect of the rough zone on cavitation is slightly weakened with the increase of the length of 3mm,9 mm,and 15 mm.When the cavitation number is reduced to σ=0.24,as the length value becomes larger,the effect of suppressing cavitation is slightly weakened;increasing the length o f the rough zone will slightly improve the effect of suppressing the volume of cavitation.This is because when the cavitation development is weak,the former part of the rough zone plays a role in suppressing cavitation.The longer the rough zone,the gre ater the interference to the rear,which is not conducive to the inhibition of cavitation.With the development of cavitation,the longer the rough zone,the stronger the control range and suppression ability of the cavitation volume. |
PDF Full Text Request