Study On The Flow Characteristics Of Oil Film On The Wall Under The Disturbance Of Micro-droplet Impact

In the working process of the oil-gas micro-lubrication system,the high-pressure gas is used to transport the lubricating oil to the lubrication area in the form of microoil droplets,and a thin oil film is formed on the friction surface,in which the air flow plays the role of conveying and cooling.With the deepening of the concepts of carbon neutralization and green manufacturing,the research work of oil-gas micro-lubrication system with low-carbon and environmental protection characteristics has attracted more and more attention.The formation quality of lubricating oil film is the key to ensure the lubrication effect of friction pairs and improve the service life of equipment.at the same time,it also involves multi-scale physical problems under the influence of air flow and different external environment.Related studies show that under the impact disturbance of high pressure gas and micro-oil droplets,there is bubble entrainment behavior in the process of oil film formation and flow,and the existence of bubbles will accelerate the oxidation deterioration of oil film and destroy the integrity of oil film.At present,the research on the film-forming flow behavior of micro-oil droplets impacting on the wall is still in the perfect stage,and the study of oil film flow under the influence of bubble entrainment is still not deep enough.In this paper,the study on the flow characteristics of oil film on the wall under micro-droplet impact disturbance is of great significance for the further study of the micro-flow behavior of oil film and the identification of the dynamic mechanism of oil film flow with bubbles,as well as to improve the lubrication effect.The main contents and conclusions of this paper are as follows:(1)Experimental scheme design and rationality verification of oil-gas microlubrication.First of all,the design and overall architecture requirements of the oil-gas micro-lubrication oil film flow experimental system are explained,the oil-gas microlubrication oil film flow experimental platform is built,and the specific experimental steps and auxiliary equipment are introduced.finally,the oil-gas micro-lubrication oil film flow experiment is carried out to verify the rationality and reliability of the experimental scheme.The study shows that the experimental scheme of oil-gas microlubrication oil film is reasonable and feasible,and the overall work of the experimental platform is stable,safe and reliable.(2)Experimental study on film-forming flow characteristics of oil-gas trace lubricating oil droplets impacting on the wall.The effects of gas supply pressure and oil supply on the flow characteristics of oil film on the wall are investigated,and the macroscopic process of morphological evolution of micro-oil droplets after hitting the wall is discussed.the effects of different gas supply pressure and oil supply on the spreading length,speed and thickness of oil film are analyzed.The results show that there are two stages in the film-forming flow of micro-oil droplets hitting the wall.The spreading area of the oil film shows a circular diffusion growth in the initial flow stage,and then develops into a finger shape profile at the front end of the oil film flow,and the gas supply pressure promotes the formation of the finger shape profile at the front end of the oil film.The oil supply is the main factor affecting the oil film thickness,and the gas supply pressure has a positive effect on the oil film thickness.with the increase of oil supply,the oil film spreading length and speed have no significant change,but the oil film thickness is significantly increased.Increasing gas supply pressure can obviously change the oil film spreading length and speed and reduce the oil film thickness,and under the condition of low gas supply pressure,increasing gas supply pressure can slightly increase the oil film thickness.There is a defined threshold for the effect of gas supply pressure and oil supply on the flow stability of oil film.when it is lower than this threshold,the fluctuation intensity of oil film increases with the increase of gas supply pressure and oil supply.Oil film fluctuation intensity fluctuates near the threshold value.(3)Numerical simulation of oil film flow on the wall under the influence of air flow.A two-dimensional numerical model of oil film flow on the wall under the influence of air flow is established by using the VOF method,focusing on the structural changes of the internal and external flow field of the oil film flow on the wall.The results show that the vortex formed in the oil film changes the direction of fluid flow in the oil film and promotes the uplift of the oil film.The velocity distribution gradient inside the oil film is induced by the high speed region of the gas flow field at the back end of the oil film.with the increase of the thickness of the oil film,the range and intensity of the high speed region of the air flow field increase,and only disturb the surface of the middle and back end of the oil film.(4)Numerical simulation of the influence of bubble entrainment behavior on the flow characteristics of oil film.The influence of bubbles on the flow characteristics of oil film is emphatically investigated,the interaction process between bubbles and the surface of oil film is discussed,and the effects of bubbles on the velocity distribution of oil film and the fluid and wall pressure in the cavity field are analyzed.The results show that the deformation and migration of the oil film entrainment bubble induce the velocity disturbance of the micro-flow field around the bubble,which leads to the nonuniform velocity gradient distribution at the gas-liquid interface,and then leads to the morphological fluctuation of the oil film surface.the pressure stratification and the change of fluid movement direction in the "depression area" caused by capillary wave propagation and motion are the main reasons for the rupture of oil film.When the oil film is ruptured,there are obvious positive and negative pressure fluctuations in the hole of the oil film,and the wall near the bubble will bear a certain alternating load.