Study On The Flow Behavior And Lubrication Characteristics In Oil-air Lubrication For Line Contact

In the process of oil-air lubrication,the lubricant moves forward along the wall of the tube under the action of the high speed air,and the lubricant is sprayed to the lubricating point by small droplets separated from air.The advantage of oil-air lubrication is to adapt to all kinds of harsh conditions.At present,the research of oil-air lubrication mostly focuses on the practical application of bearing,high speed motorized spindle and so on.Up till now,there is lack of study on oil-air lubrication theory.In order to deeply study the principle of oil-air lubrication,it is necessary to start from the most basic research on oil-air lubrication.In this paper,the oil-air lubrication flow behavior and lubrication characteristics of line contact were studied.The main contents and conclusions are as follows.1)Used numerical simulation method to observe the flow field of oil-air lubrication.The oil-air lubrication system was simplified to a two-dimensional CAD model.The numerical simulation was carried out by CFD software FLUENT.Multiphase(VOF)Model and RNG Model were chosen,and physical parameters and boundary conditions were set.The flow field distribution and the volume distribution of the oil-phase on the surface were observed.The laws of oil-air two-phase flow and pressure distribution were discussed.It was found that the volume fraction of the oil-phase on the surface of the ring was fluctuating greatly.And its rationality was verified.2)Based on the above two-dimensional CFD model,the numerical simulation of oil-air lubrication for line contact with different factors was carried out.Based on the analysis of the oil-air two-phase flow and the volume distribution of the oil-phase on the surface of the ring,the characteristics of the oil-air two-phase flow were obtained under different factors,such as the quantity of oil supply,the velocity of air supply,the speed of rotation,the roughness of surface and the position of jet.It was found that too much oil supply or too little air supply would cause the accumulation of lubricating oil in the ring surface,which leads to the large volume fraction of oil phase on the surface of the ring.And when the oil supply is too little or the air supply is too much,it was difficult to observe the lubricating oil in the entrance area,and the volume fraction of oil phase was low.The position of jet changed the oil-air lubrication flow behavior through the change of the pressure distribution in the in the entrance area,and changed the volume fraction of oil phase on the surface of the ring.With the increase of surface roughness or the increase of viscosity,the volume fraction of oil phase on the surface of the ring would be increased.And the effect of viscosity and rotating speed were small.3)The experiment was conducted to study the effects of different factors on the oil-air lubrication for the line contact.The lubricating characteristics of the oil-air lubrication for line contact were discussed by comparing the friction coefficient of different quantity of oil supply,speed of rotation,position of jet and so on.It was found that when the velocity of air supply is too low,the lubricating oil can not be sprayed to the surface of the ring.The friction pair is close to dry friction and the friction coefficient is large.When the fuel supply is insufficient,the friction coefficient is larger.When the supply amount is sufficient,the friction coefficient decreases rapidly.And continue to increase the supply,the friction coefficient remained stable.When the position of jet is good,the lubricating oil is easier to spray to the surface of the ring,and the friction coefficient is smaller.The rotating speed has a great influence on the friction coefficient,and the friction coefficient will be decreased with the increase of rotating speed or load.