油滴/金属壁面正碰撞的油膜动力学特性

Oil film dynamic characteristics during oil droplet’s normal impact onto metallic surface

为诠释轴承腔中润滑油滴与腔壁碰撞形成的沉积油膜流动铺展问题,采用流体体积(VOF)方法建立了油滴与金属壁面正碰撞的三维数值分析模型,在试验获得油滴与壁面静态接触角的基础上,通过数值计算,探讨了沉积油膜动态铺展和回缩过程,以及油滴直径和碰撞速度对沉积油膜铺展直径、特征厚度、铺展速度以及碰撞力等油膜动力学特性的影响。结果表明:沉积油膜在最大铺展直径时呈中心微凹的圆盘形状,进入回缩阶段后则蜕变为边缘薄中心厚的圆盘形状;沉积油膜的回缩速度和回缩阶段的碰撞力都非常小,其值接近于0,并保持基本恒定;随着油滴直径的增大,沉积油膜铺展直径、特征厚度、铺展速度以及碰撞力均增大;随着碰撞速度的增大,油膜铺展直径和碰撞力增大,特征厚度却随之减小。与相关试验结果的对比,验证了提出的数值分析模型的可靠性和正确性。

To explore the spread behavior of the deposited oil film formed by droplethousing impact in aero-engine bearing chamber,a three-dimensional numerical model was presented using volume of fluid(VOF)method to predict the oil/air two-phase flow during the normal impact of oil droplet onto a smooth stainless steel surface.The static contact angle between droplet and surface was measured by experiment.The dynamic spreading and recoiling process of deposited oil film during the normal impact was analyzed,and the effects of droplet diameter and impact velocity on dynamic characteristics such as spread diameter,nominal film thickness,spread velocity and impact force were discussed.The calculation results showed preliminarily that at maximum spread diameter the film appeared to be a flat disk with slightly concave center,and in the recoiling period,it appeared to be a disk with thin rim and thick center.The recoiling velocity of film and the impact force in the recoiling period reduced nearly to 0 and remained approximately constant.The oil film spread diameter,nominal film thickness,spread velocity and impact force increased with the increasing droplet diameter.The spreading diameter and impact force increased with the increasing impact velocity of droplet,whereas the nominal film thickness decreased.Finally,the reliability and correctness of the model presented was validated by comparing with relevant experimental data.