【作者】 刘翔；

【导师】 林晓辉；

【作者基本信息】 东南大学 ， 机械设计及理论， 2017， 硕士

【摘要】 水润滑螺旋槽轴承具有粘-温特性好、振动噪声小、旋转精度高、磨损小、加工表面质量稳定和不污染环境等优点。因此,以水润滑螺旋槽轴承作为高速轴支承的研究已成为国内外研究的热点。本文阐述了水气润滑技术与理论的发展及研究背景和意义,将空化流视为水和气泡组成的两相流,水视为不可压缩流体,空化流中气泡视为离散的可压缩的规则圆形球体。本文模型基于壁面紊流定律、两相流Navier-Stokes方程、连续性方程推导出了考虑界面效应和惯性效应的水气两相流润滑的广义Reynolds方程和能量方程,利用粒子数守恒原理导出了描述气泡分布演化状况的群体平衡方程(Population-Balance Equation),通过气泡受力平衡关系建立了气泡速度控制方程。最终建立了高速螺旋槽推力轴承紊态空化流热动压润滑的理论模型,该模型同时考虑了高速工况下的紊流效应、惯性效应、热效应、气液界面效应以及气泡在水中的破裂与聚合机制,并对模型中各控制方程的数值计算方法进行了探讨,绘制了求解程序的逻辑框图以及编写了程序代码。采用求解程序对高速螺旋槽推力轴承紊态空化流热动压润滑的理论模型进行了数值模拟计算,给出了螺旋槽水膜压力分布和温度分布图,并且描述了气泡在空间坐标和内部坐标(内部坐标被定义为气泡体积)的分布情况,同时分析了螺旋角、转速、槽深对螺旋槽动压推力轴承静特性以及最大温升的影响。数值模拟计算结果表明,对于高速螺旋槽动压推力轴承,惯性效应可能使螺旋槽中出现贫水现象,而空化效应使螺旋槽中分布大量的气泡。因此,惯性效应和空化效应将导致承载力和摩擦力矩下降。高速工况下,惯性效应将增加流体的流速,流体与封水边壁面的碰撞将更加剧烈,因而在考虑惯性效应时温度有所上升;而空化效应产生大量的气泡,水与气泡之间存在动量交换,流体能量减少,将导致温升有所下降。随着转速的增加,螺旋槽水膜压力增加,水中含有的“微气核”长大变成气泡的数量减少,空穴率降低;气泡主要集中在螺旋槽低压区域;在高转速情况下,气泡之间的破裂和聚合效应将会更加明显,从而平均气泡直径有所降低,小气泡的数密度增加。模型计算得到的静特性以及气泡分布变化规律与实验值有很好的吻合。更多还原

【Abstract】 Water-lubricated spiral groove bearing are expected to be widely used because of convenience,green,safe and energy saving.This paper described the development of water-gas lubrication technology and theory,also expounded research background and significance of this topic.Based on the two-phase flow theory,regarded the cavitation flow as two-phase flow,which compose by pure water that regarded as continuous incompressible fluid and bubbles that seen as discrete compressible round sphere.Based on the generalized law of wall,N-S equations,the continuity equation,this paper derived the generalized Reynolds equation and the energy equation;deduced the Population-Balance Equation by using the conservation of particles to describe the evolution of the bubbles distribution;utilized the force equilibrium relationship to establish the bubble speed control equation.And then,a theory model of a high-speed spiral groove dynamic pressure thrust bearing lubrication of water and gas two-phase turbulent flow which considered turbulence effect,inertial effect,heating effect,interface effect and the breakage and the coalescence of bubbles was established.Numerical calculation methods for the model were discussed in this paper and MATLAB code was compiled to solve the model.The pressure distribution,temperature distribution and the bubble distribution of the spiral groove thrust bearing were shown in this paper.The paper also analyzed the influence of the helix angle,the rotational speed and the depth of groove on the main static characteristics of bearing.Numerical simulation results show that the loading capacity and the friction torque decreases when considered the inertia effect and cavitation effect,the reason are the lubricant is thrown out of spiral groove due to inertia effect and the momentum transfer between water and bubbles created by cavitation surface tension when considered cavitation effect.In high speed condition,the maximum temperature rise is lower than the pure water lubrication but higher than the model which ignored the inertial effect.Because the inertial effect would increase the flow rate of fluid,the collision between fluid and wall would become more intense,so the maximum temperature would rise when consider the inertial effect;on the other hand,the energy transfer between water and bubbles causes the maximum temperature fall when considered cavitation effect.Bubble spread mainly concentrated in the divergent area.With the increase of the rotational speed,the pressure of the water film increases,so the number of micronucleus decreases,finally causes the gas fraction decreases;At the same time,the breakage and coalescence effect would become more and more fierce in the case of rational speed,the average bubble diameter would get smaller but the number gets more.The static characteristic of the spiral groove bearing and the evolution of the bubble distribution are in good agreement with the experimental data.更多还原