Effect Of The Geometric Parameters At Inlet Of Inducer And Itself On Cavitation Characteristics Of Centrifugal Pump

Cavitation is an unavoidable flow phenomenon during the operation of a centrifugal pump.It refers to the process in which the normal-temperature liquid forms vapor bubbles in the low-pressure area of the flow field.Cavitation is usually harmful to pumps.On the one hand,cavitation causes a dramatic drop in the head and efficiency of the pump,which affects the energy conversion of the fluid inside the pump.On the other hand,cavitation is a source of denudation on the surface of fluid mechanical materials.The pressure energy and heat energy released at the moment when the vapor bubbles burst seriously damages the surface of the pump blade and shorten the service life of the pump.At the same time,cavitation also affects the unsteady or dynamic response characteristics of the flow.Therefore,how to restrain the occurrence and development of cavitation more effectively has been a hot issue in the field of hydraulic machinery.In this paper,a certain type of booster centrifugal pump is used as the research object.Relying on RNG k-?turbulence model and the Zwart cavitation model based on the Rayleigh-Plesset equation,the cavitation steady and unsteady of the model pump are simulated and verified with the experimental results.The method and mechanism of improving the cavitation performance of a centrifugal pump by changing the axial matching relationship between the inducer and the suction chamber and changing the wedge angle on meridian plane of inducer are studied.The development of cavitation in the centrifugal impeller and the front inducer,the effect of cavitation on energy conversion,and the pressure pulsation characteristics of the centrifugal pump in the cavitation flow field are studied in depth.The main research contents and conclusions of this paper are as follows:1.The evolution and development process of cavitation in centrifugal pump are revealed by analyzing the distribution cloud of cavitation volume fraction in centrifugal pump,the static pressure distribution cloud of suction surface of inducer blade and the pressure pulsation characteristics of inlet and outlet of inducer and centrifugal impeller under different net positive suction head available.At the same time,the differences of cavitation evolution under different flow conditions are compared and analyzed.The results show that the flow rate has a certain influence on the initial point of cavitation of the centrifugal pump,and the cavitation is most likely to occur with large flow rate,followed by design flow rate,and not easily with small flow rate.The large flow rate is the most likely to cause cavitation,the design flow rate is the second,and not easily with small flow.Cavitation first appears in the form of the formation of vapor in the local low pressure area of the liquid flow field at the intersection of the inlet side and the flange of the inducer.With the aggravation of cavitation,the vapor gradually extends along the liquid flow to the outlet of the inducter blade,until it fills the entire flow channel of inducer and centrifugal impeller.The distribution area of the static pressure on the suction surface and in the flow channel of the inducer corresponds to the distribution area of the vapor in the inducer flow channel.The cavitation flow causes the pressure pulsation at the inlet and outlet of the inducer and the centrifugal impeller fluctuate violently and the flow instability is strengthened.2.Effect of axial matching between inducer and suction chamber of centrifugal pump on cavitation performance.Five groups of centrifugal pump design schemes are selected,with the ratio of the degree of axial extension of the inducter into the suction chamber and the axial distance of the inducer wheel hub are 0?original scheme?,1.6%,3.2%,4.8%,and 6.4%,respectively.The results show that the proper extension of the inducer into the suction chamber can change the flow state of the fluid at the interface between the inducerl and the suction chamber,and provide a more stable inflow condition for the inducer.At the same time,the inducer does work on the liquid in advance,which provides a good suction environment for the impeller and improves the cavitation performance of the centrifugal pump.With the increase of axial penetration,cavitation performance is better,but the effect tends to be stable after reaching a certain degree.3.Effect the wedge angle on meridian plane of inducer on cavitation performance of centrifugal pump.The centrifugal pumps with five wedge angle on meridian plane of inducer?₂=3°,4°,5°?original scheme?,6°,and 7°are selected for analysis.The results show that the thinner the blade thickness and the blade root of the inducer are,the less the squeezing of the blade on the liquid is,the lower the fluid flow rate is,the higher the pressure is,and the better the cavitation performance is.Therefore,the cavitation performance of the centrifugal pump can be improved by appropriately reducing the wedge angle??₂?on meridian plane of inducer.Considering the sensitivity of reducing the value of?₂ to improve the cavitation performance of the centrifugal pump and the manufacturing process and strength requirements of the inducer,the optimal scheme is determined when the wedge angle on meridian plane of the centrifugal pump inducer is?₂=3°.