气泡夹带对壁面油膜流动特性的影响

The effect of bubble entrainment on the flow characteristics of the oil film on the wall

油-气润滑系统工作过程中,润滑油膜受微油滴冲击和压缩空气扰动影响易形成气泡夹带现象,气泡夹带行为将对壁面润滑油膜层的形成及流动过程产生重要影响。基于VOF数值模拟方法,对含气泡油膜沿倾斜壁面的流动行为进行研究,考察了气泡的存在对油膜形态和流动速度的影响规律,以及气泡破裂阶段空腔邻域内流体压力变化特性。研究表明,油膜夹带气泡的形变和迁移诱发气泡周围微流场的速度扰动现象,导致气液界面处产生非均匀速度梯度分布,进而引发油膜表面的形态波动。气泡发生破裂时,油膜空穴部位发生明显的正负压力波动现象,气泡附近壁面将承受一定的交变载荷作用。

During the operation of an oil-air lubrication system,the lubricating oil film is affected by the impact of micro-oil droplets and the disturbance of compressed air,which is prone to bubble entrainment.The bubble entrainment behavior will have an important impact on the formation and flow process of the lubricating oil film on the wall.Based on the VOF numerical simulation method,the flow behavior of the bubble-bearing oil film along the inclined wall was studied,and the influence of the bubbles on the shape and flow velocity of the oil film,as well as the pressure change characteristics of the fluid in the vicinity of the cavity during the bubble burst stage were investigated.These studies have shown that the deformation and migration of bubbles entrained in the oil film induce velocity disturbances in the micro-flow field around the bubbles,resulting in a non-uniform velocity gradient distribution at the gas-liquid interface,which in turn triggers morphological fluctuations on the oil film surface.When a bubble bursts,obvious positive and negative pressure fluctuations occur in the cavity of the oil film,and the wall near the bubble will bear a certain alternating load.