超薄含水油膜Couette流润滑特性的分子动力学模拟

Molecular Dynamics Simulation of Lubrication Characteristics of Ultra-thin Hydrous Oil Film under Couette Flow

基于分子动力学方法,建立超薄含水柴油膜的全原子分子模型,进行不同含水率下油膜Couette流的润滑特性研究。在相同剪切速度作用下,分析含水油膜的微观结构、速度分布、整体键取向参数、剪切黏度等性质。发现不含水时油膜形成了类固体层,不具有流动性,且在剪切过程中黏度值下降,即表现出剪切时间稀化现象;而含水工况下,油膜出现分层结构,流速符合Couette流的流动特性;且含水率越高,油膜的分层现象越明显,链烃的有序性越强,致使油水混合薄膜的剪切黏度值也越低,呈现出非牛顿流体性质,此时油膜固有的剪切稀化特性被削弱。研究表明,水分子由于具有较强的分子间作用力,能促使油膜中的有机分子重新排布,从而对油膜的润滑性能产生较大改变。

All-atom molecular models of ultra-thin hydrous diesel oil film were built based on molecular dynamics simulation method,and the lubrication properties of the oil films with different water cuts under Couette flow were investigated.The micro-structure,velocity distribution,global orientational order parameter and shear viscosity of the ultra-thin lubrication film under the same shear velocity were researched.The results show that for the anhydrous oil film,its behavior is solid-like without fluidity,and it shows a shear thinning property during the shear process.However,for the hydrous ultra-thin oil film,the film shows a layered structure and its flow velocity is confirmed to Couette flow.When the water cut is raised,the layered structure becomes more obvious and the chain hydrocarbons are more ordered.These lead to a lower shear viscosity of the ultra-thin film,which shows a non-Newtonian fluid property,and the inherent shear thinning property of the oil film is weakened.This research shows that,because of the strong intermolecular force,the water molecules can rearrange the organic molecules in the oil film,thus greatly changs the lubrication properties of the ultra-thin oil film.