喷射油滴沉积油膜的流动铺展特性研究*

航空齿轮和航空发动机主轴轴承都采用喷油润滑的方式进行润滑,喷射油滴与机械零件表面碰撞后形成的沉积油膜的流动特性影响着机械零件的润滑状态和功能。由于有关喷射油滴与固体表面碰撞形成沉积油膜及其流动铺展特性研究较为鲜见,已有的相关研究集中于液滴/固体壁面正碰撞条件下的非油类液膜流动分析,故而对机械零件相关润滑分析计算支持极为有限。采用VOF方法建立了喷射油滴/固体壁面斜碰撞及其沉积油膜流动铺展数值分析模型,通过试验研究对数值分析模型进行了修正,进而基于此数值分析模型分析了航空传动零件润滑等效条件下喷射油滴/固体壁面斜碰撞沉积油膜流动铺展特性,通过与国外相关试验结果的对比验证了所提出的数值分析模型的正确性和实用性。所开展的喷射油滴沉积油膜的流动铺展特性研究,为航空机械零部件润滑计算提供了技术方法和基础数据,对于实现航空机械零部件精确润滑设计有明显的工程意义。     

运动油滴/固体壁面斜碰撞及油膜铺展的数值模拟

基于Volume of Fluid(VOF)方法建立了运动油滴/固体壁面斜碰撞及油膜铺展的数值计算模型,分析了运动油滴/固体壁面斜碰撞后的油膜铺展特征,讨论了油滴入射角、碰撞速度和油滴直径等对油膜铺展特征的影响规律。研究结果表明,前铺展因子随着入射角的减小而增大,随着碰撞速度和油滴直径的增大而增大;后铺展因子绝对值随着入射角和油滴直径的减小而减小,而碰撞速度对其几近没有影响,同时在入射角和油滴直径较小的情况下较易观察到铺展油膜的滑移现象;数值模拟结果与试验结果较好的吻合性证明了该数值模拟方法的正确性。     

弹流接触单液滴润滑特性分析

在油气润滑系统中,润滑油以分散的微油滴来为摩擦副供油建立油膜。不同的固-液界面形成不同的微液滴铺展半径。基于此建立了简化的单个微油滴供油弹流润滑模型,模拟了定体积微油滴润滑成膜过程。结果表明:一定体积的微油滴供油时,其润滑效果与其初始铺展半径有关,存在一定范围铺展半径使接触区具有良好成膜能力;最佳铺展半径范围受卷吸速度和润滑油黏度影响。     

加工薄壁零件的消振夹具

对于车床强迫振动,找到振源较容易,车削过程的自激振动亦有许多研究报导,但是薄壁零件的自激振动和消除方法却研究很少。本文依据振动原理设计消振夹具用于消除薄壁零件车削过程的自激振动,并介绍应用实例。一、消振夹具设计当随时间变化的激搌力作用于弹性系统时,就产生强迫振动,实际振动很复杂,可以分解为径向和轴     

压路机振动轮维修要点

压路机振动轮在振动马达的驱动下,偏心块与轴一起高速旋转,产生激振力(离心力),使振动轮以一定的频率和振幅振动,对土壤进行挤压,从而达到压实路面的效果。 对振动轮而言,振动轴承是靠偏心块飞溅起来的润滑油来润滑的,采用骨架油封密封润滑油,它不可避免地要与润滑油长     

液滴撞击不同浸润性倾斜壁面的动态特性

液滴撞击到固体壁面是一种广泛存在自然界中以及各个行业领域中的物理现象。采用化学刻蚀方法制造不同浸润性壁面,随后利用高速摄影技术及图像处理方法对单个润滑油液滴撞击倾斜壁面开展实验研究。主要考察了壁面浸润性,倾斜角度及撞击速度对液滴铺展行为及流动特性的影响规律。实验结果表明,液滴撞壁后的动态行为可分为2个阶段。第一阶段为剧烈形变阶段,大约为碰撞壁面后的前20 ms,液滴主要经历了迅速铺展然后回缩的过程,此阶段中浸润性对达到最大铺展长度所需的时间无明显影响,但随着浸润性变差,液滴铺展程度下降;随后为稳定铺展的第二阶段,液滴进行较为缓慢的二次铺展,浸润性变差会抑制液滴的铺展,倾斜角的增大促进铺展发生,两者的关系决定了铺展能否发生以及铺展的速率。     

激振频率对裂纹梁系统振动特性的影响

用ZK-4VIC型振动与控制实验台和ZK-1型电动式激振器分别对相同的Q235裂纹梁系统加载大小相同频率不同的简谐激振力(F=1.12N,w=17Hz、19Hz、21Hz、23Hz),对裂纹梁的振动疲劳过程进行模拟。记录实验过程中裂纹梁的振动幅值随时间变化的趋势,分析在不同激振频率的激振力作用下,疲劳裂纹对裂纹梁振动特性的影响。结果表明:加载简谐激振力的激振频率与固有频率的关系对裂纹梁系统的振幅变化影响显著;裂纹产生后,刚性系统受裂纹的影响大于柔性系统受裂纹的影响,寿命较短;刚性系统比柔性系统更容易从振动变化上发现裂纹故障的存在。     

基于变速器振动特性的齿轮异常磨损分析

变速器由于各种激振产生复杂的振动,不仅关系到乘坐舒适性,对传动系统各零件寿命和可靠性都有重要的影响。在设计开发阶段考虑变速器的激振来源以及内部零件与外部换挡操纵的模态,可有效改善变速器相关振动问题。通过某机械式变速器整车耐久试验中挡位齿轮结合齿早期异常磨损引起的换挡手柄抖动分析,从振动特性为出发点,推论出主减齿轮为激振源,一轴总成、平衡块等产生叠加共振。提出改善对策并通过了试验验证。     

振动时效技术机理

（接上期） 7 振动时效工艺过程 振动时效处理过程是将激振器刚性夹持在被处理零件的适当位置,首先根据零件大小,形态和夹持情况来调节激振频率,最好使零件在其固有频率下进行共振,然后应根据零件所需动应力或振幅的大小来调节激振力。零件的振动状态和动应力,可用测量振动和应力的仪表来检测。通常将感受元件（加速度计或速度计）接于被振物体上,振动时,感受元件把接收到的振动信号送往测试仪表,经放大并指示出各种所需的参数值。振动状态的主要指示参数是振幅、频率和振型。振动状态和激振力的控制是通过激振器的控制装置来实现…     

YZT25吨超重型拖式振动压路机

YZY25吨超重型拖式振动压路机是经济建设中的特大型水利,公路,铁路,机场,港口,水电站等工程,需要激振力大,生产率高的压实机械。该机就是专门为这些工程项目而设计制造的。 YZT25超重型拖式振动压路机集我厂多年之经验,振动轮内采用新型振动轴承,飞溅润滑,     

球－盘静态接触间隙条件下润滑油微液滴铺展实验研究

为研究润滑油微液滴润滑机制,采用多光束干涉技术对球-盘静态接触下润滑油微液滴的铺展流动现象进行实验观察。结果表明：在球-盘接触构成的微间隙周围毛细力诱导微液滴铺展流动,微液滴铺展速度随液滴体积的增大而增大,随液滴黏度的增大而减小;润滑油微液滴在高表面能界面上具有较大的铺展速度;当润滑油的表面张力较小时,液滴的初始铺展半径变大,铺展距离明显减小,且产生二次铺展现象。     

Elastohydrodynamic Lubrication with Oil Droplets

In oil–air lubrication, lubricants are supplied in the form of oil droplets to tribo-pairs. Numerical work has been carried out to investigate transient EHL characteristics when a series of oil droplets are entrained along the center line of the contact zone. Results show that the spacing distance between oil droplets is an important parameter for continuous EHL film formation. For oil droplets with the same volume, the effective lubrication time increases first and then decreases as the droplet distance increases. An optimum droplet distance can be found for the maximum effective lubrication time with continuous EHL films. Moreover, entrainment speed, lubricant viscosity and oil/solid interface can also affect the effective lubrication time significantly and change the optimum droplet distance accordingly. Numerical results showed a close correlation to the experiments. This study is useful to basic understanding of lubrication by limited lubricant supply.     

A study on the behavior and heat transfer characteristics of impinging sprays

The spray/wall interaction is considered as an important phenomenon influencing air-fuel mixing in the internal combustion engines. In order to adequately represent the spray/wall interaction process, impingement regimes and post-impingement behavior have been modeled using experimental data and conservation constraints. The modeled regimes were stick, rebound, spread and splash. The tangential velocities of splashing droplets were obtained using a theoretical relationship. The continuous phase was modeled using the Eulerian conservation equations, and the dispersed phase was calculated using a discrete droplet model. The numerical simulations were compared to experimental results for spray impingement normal to the wall. The predictions for the secondary droplet velocities and droplet sizes were in good agreement with the experimental data.     

Modeling of diesel spray impingement on a flat wall

To understand the transient behavior of droplets after impingement in a diesel engine, a numerical model for diesel sprays impinging on a flat wall is newly developed by the proposition of several mathematical formulae to determine the post-impingement characteristics of droplets. The new model consists of three representative regimes such as rebound, deposition and splash. The gas phase is modeled in terms of the Eulerian conservation equations, and the dispersed phase is calculated using a discrete droplet model. To validate the new model, the calculated results are compared with several experimental data. The results show that the new model is generally in good agreement with the experimental data. Therefore, it is thought that the new model is acceptable for the prediction of transient behavior of wall sprays.     

Dynamical analysis of droplet impact spreading on solid substrate

This paper investigates the impact spreading of a droplet on a solid substrate using numerical simulation on the basis of a volume-of-fluid (VOF) model. The process of droplet spreading is described, the analysis of low speed and high speed droplet spreading, and more than one droplet spreading simultaneously is performed. The pressure, velocity, and spreading factor during the droplet spreading are reported. According to the spreading factor’s evolvement, the process of droplet spreading can be classified into spreading phase and recoiling phase. The spreading factors are almost the same at the low speed droplet spreading; however, the pressures on the substrate are quite different and air entrainment may be found as the impact speeds in a certain range. The impact speed impacts on the spreading factors in high speed droplet spreading. The spreading factor obviously increases with increasing impact speed; however, splashing will appear in the status when the speed is high enough in the high speed droplet spreading. The distance between the neighbor droplets affects the film’s quality, and only the distance between the static diameter and the maximum diameter can ensure the film’s quality. The results could help in understanding the process of droplet spreading and provide advice on the operation of a spray coating process.     

Dynamical analysis of droplet impact spreading on solid substrate

This paper investigates the impact spreading of a droplet on a solid substrate using numerical simulation on the basis of a volume-of-fluid (VOF) model. The process of droplet spreading is described, the analysis of low speed and high speed droplet spreading, and more than one droplet spreading simultaneously is performed. The pressure, velocity, and spreading factor during the droplet spreading are reported. According to the spreading factor’s evolvement, the process of droplet spreading can be classified into spreading phase and recoiling phase. The spreading factors are almost the same at the low speed droplet spreading; however, the pressures on the substrate are quite different and air entrainment may be found as the impact speeds in a certain range. The impact speed impacts on the spreading factors in high speed droplet spreading. The spreading factor obviously increases with increasing impact speed; however, splashing will appear in the status when the speed is high enough in the high speed droplet spreading. The distance between the neighbor droplets affects the film’s quality, and only the distance between the static diameter and the maximum diameter can ensure the film’s quality. The results could help in understanding the process of droplet spreading and provide advice on the operation of a spray coating process.     

超亲水-水下疏油铜网润湿性及油水分离研究

为研究铜网表面润湿性对油水分离性能影响,以金属氧化法处理后的超亲水-水下疏油铜网为油水分离介质,讨论处理前后空气中水、水下油接触角变化情况。分析不同油样、不同含油体积分数、不同滤网目数对油水分离性能影响。利用Cell Registers功能进行数值模拟,分析空气中水滴铺展和水下油滴聚集状态。结果表明:处理后的铜网表面形成的Cu(OH)2微结构在空气中呈超亲水性,随着铜网目数增加,水下疏油性增强;油水两相密度差越大、黏度差越大以及含油体积分数越大、铜网数目越大,均能得到较高的油水分离效率;亲水表面的水滴铺展系数随时间增加而逐渐增大,水下疏油表面的油滴铺展系数先缓慢增大后稳定不变。超亲水-水下疏油铜网的应用对提高和强化油水分离性能具有较好的发展前景。     

基于MPS方法的二级齿轮箱飞溅润滑特性研究

飞溅润滑时,二级传动齿轮箱内部润滑油流场分布情况十分复杂,传统有限元方法难以对其进行可视化仿真分析,在模型处理、算法选用、网格划分和计算工作量等方面存在诸多问题。基于充分的调研与大量的前期计算分析,利用移动粒子半隐式（MPS）法对轨道车辆用二级传动齿轮箱的飞溅润滑特性进行研究。分析了不同输入轴转速、初始润滑油油量和环境温度下齿轮箱内部润滑油的流场特性,实现了齿轮箱飞溅润滑的可视化计算;分析了不同工况下齿轮啮合点的油液粒子数时域变化情况,发现啮合处粒子数与转速关系不大,与初始油量成正相关,40 ℃时啮合处滑油粒子数最多,润滑效果最好;分析了各工况的齿轮箱搅油功率损失情况,发现搅油功率损失与输入轴转速和初始滑油油量成正相关,与环境温度的提高成负相关,且均为非线性变化。     

Investigation of condensate droplet movement in marangoni condensation of ethanol-water mixtures by infrared thermography

Marangoni condensation is a phenomenon that occurs during the condensation of a positive system with binary vapor mixtures. Applying infrared thermography to the investigation of Marangoni condensation could not only help to obtain quantitative data on droplet movement but also establish the relationship between the droplet velocity and surface temperature of condensate droplets. In this study, the droplet movement in Marangoni condensation of ethanol-water mixtures was experimentally investigated by infrared thermography. The effects of vapor concentration, impinging cooling water temperature, and vapor velocity on droplet velocity were investigated, and the relationships between droplet velocity, temperature gradient, and surface tension gradient were studied. The results indicated that the droplet velocity first increased and then decreased with the increase in the droplet radius. The maximum droplet velocity decreased with the increase in vapor concentration and vapor velocity. As impinging cooling water temperature increased, the droplet velocity decreased, and the decline was more obvious at the high impinging cooling water temperature. In addition, the droplet velocity increased and then decreased with the increase in the surface temperature gradient and surface tension gradient.