Experimental Research On Cavitation Erosion Of Impeller Materials

There are lots of factors that need to be considered in pump and other hydraulic machinery design,due to the impeller immersed in the liquid.In addition to the mechanical properties,the functions of thermal effects,cavitation erosion and corrosion are also need to be thought of when choosing impeller materials.The prevention of cavitation erosion is very important to the designer.The collapsing process is very complex and has the characteristic of multiphase,microscopic,transient and stochastic.What's more,the related theoretical modeling and experimental research are often very complicated and difficult.There are many factors that affect material cavitation erosion resistance.Cavitation erosion prediction is still a challenge.It is important to analyze hydrodynamics to predict the strength of cavitation damage and the location of cavitation erosion in the field of mechanical engineering.In recent years,there are many studies attempting to estimate cavitation erosion energy and its damage to the material.It is hoped that the designer can reliably predict the cavitation erosion rate of hydraulic equipment under specific conditions.A large number of experimental studies are aiming at illustrating the mechanism of material cavitation erosion,and finding ways to improve the performance of materials.In this paper,cavitation erosion test by ultrasonic vibration method was carried out.The cavitation erosion resistance of metal materials and coating materials had been studied.The influence of material factors on cavitation erosion resistance also had been analyzed.The cavitation erosion data of all materials were summarized.And then according to the different selected factors,such as the hardness of materials and fatigue resistance,the influence of various factors on the anti-cavitation erosion performance of the materials were analyzed.The micro-hardness,micro-structure and crystal structure of the samples were observed and the relationship between the micro-hardness and the cavitation erosion resistance were analyzed.The wear resistance of the material under different types of impact loads was demonstrated,and the ability of the material to withstand shock wave of cavitation impact load was revealed.Combined with a practical engineering application case,the results provided a guidance for the selection and preparation of coating materials for practical engineering application.The cavitation erosion test of hydrofoil in water tunnel was carried out,and the cavitation erosion surfaces of hydrofoil under different flow conditions were analyzed.The theory that the small size bubble can release a high-intensity pulse pressure when collapsing is only applicable to the case when the bubbles are in direct contact with the wall during the collapsing process,such as under the cavitation condition of the ultrasonic vibration.But it is difficult to be realized in the cavitating flow process,The cavitation impact strength on the hydrofoil surface in the water tunnel is much smaller than that of the ultrasonic vibration cavitation.The relationship between cavitation cloud structure and cavitation erosion of material surface was analyzed.The potential energy was released by the large-size cloud vortex,and the pressure wave released by the cavitation cloud will cause a series of cavitation behaviors leading to erosion at the position of the cloud collapse.The overall performance of the flow is mainly determined by the overall properties of the cavitation cloud,which can consequently cause the collapse of small bubbles.Cavitation erosion is closely related to the unsteady pressure pulsation.The amplitude and distribution of cavitation pulse pressure at different points on the hydrofoil surface were obtained.The cavitation pulse pressure and the cavitation erosion test results were well correlated.Combined with pulse pressure and noise measurement,cavitation phenomena at different flow velocities and cavitation numbers were observed by the help of high-speed camera.The relationship between cavitation erosion and flow parameters was analyzed.The loading position of the cavitation cloud on the surface of hydrofoil under certain cavitation number,angle of attack and velocity was summarized,which provided a basis for predicting the location and magnitude of cavitation erosion in hydraulic machinery.It is difficult to fully understand cavitation erosion from a single aspect,such as the results of material erosion test or noise measurement.The measurement of impact load,the detection of cavitation erosion points,the measurement of cavitation noise and the capture of cavitation cloud collapse by high speed camera were combined with each other.From the analysis of cavitation dynamics and material testing,the cavitation erosion can be analyzed more profoundly.At a given cavitation number,the cavitation erosion rate and noise significantly changed when the flow velocity changed,and the erosion rate due to cavitation damage was closely related to the noise.It is very important to obtain the relationship between cavitation noise and cavitation impact energy,which provides the method of the cavitation erosion monitoring under actual cavitation conditions.