油滴与深油膜正碰撞的动力学分析

Dynamic analysis of oil droplet impacting normally onto a deep pool

为揭示航空发动机轴承腔中润滑油滴与壁面油膜的碰撞特性,采用VOF方法建立了油滴与深油膜正碰撞的三维数值分析模型。通过数值计算,分析了油滴与深油膜正碰撞后溅射油膜与空腔的形貌演化与流动铺展过程,以及二次油滴的初始特性;探讨了油滴直径和碰撞速度对碰撞结果的影响。结果表明:碰撞形成的溅射油膜以油滴接触点为中心向外铺展,最终发展为冠状油膜,其间伴随有大量尺寸各异的二次油滴产生;油膜内部形成的空腔近似空间半球形状,二次油滴的直径呈对数正态分布;随着油滴直径和碰撞速度的增大,油冠高度、空腔深度和直径均增大;二次油滴直径分布区间随着油滴直径的增大和碰撞速度的减小而更加分散。与相关试验结果进行对比,验证了提出的数值分析模型的正确性与可靠性。

To explore the impact characteristics of oil droplets impacting onto the oil film inside aero-engine bearing chamber, a three-dimensional numerical model was established using VOF(volume of fluid) method to predict the air/oil two-phase flow during the normal impact between oil droplet and deep pool. The dynamic morphologies of splashing film and cavity, and the initial characteristics of secondary oil droplets were analyzed. Subsequently the effects of droplet diameter and impact velocity were discussed in detail. The results show that the splashing film produced by the impact eventually evolves into a crown film, during which a large number of secondary droplets with different diameters are formed. An approximate hemispherical cavity is formed by the discharged oil in the pool, and the diameters of the secondary droplets satisfy a log-normal probability density function. The crown height and the cavity depth and diameter increase with the increasing droplet diameter and impact velocity. The diameter interval of secondary droplet can become more dispersed with the increasing droplet diameter and the decreasing impact velocity. Finally, the correctness and reliability of the model presented were validated by comparing with relevant experimental data.