【作者】 孙昂；

【导师】 王祖温；

【作者基本信息】 大连海事大学 ， 轮机工程， 2010， 博士

【摘要】 气体润滑是依靠几微米到几十微米间隙的气膜实现对机械运动部件的支撑。与滚动轴承及液体轴承相比,气体轴承具有速度高、精度高、摩擦功耗小及寿命长等优点。然而传统结构的气体轴承存在供气压力低,承载力小,刚度低的缺点,因此只能用于轻载精密支承,然而随着现代尖端工业技术的发展,迫切需要开发重载气体润滑系统。造成传统气体轴承供气压力低的原因在于,随着供气压力、工作间隙的增大,轴承间隙内气体流速从亚音速跨越到超音速,导致间隙内气体压力急剧下降,甚至出现负压,进而影响其承载力和刚性。由于轴承间隙内的流动过程复杂,在很长一段时期内,关于静压气体轴承超音速现象的研究一般建立在一维简化分析基础上,但由于激波与边界层的相互作用,一维简化分析的结果与实际偏离很大,不能真实体现流场特性。因而,有必要深入研究高供气压、大间隙气体轴承内的超音速间隙流动的机理,为开发高压重载气体轴承奠定理论基础。本文采用理论分析、数值模拟和实验相结合的方法,借助fluent软件平台,建立精确的流场模型,对间隙内流动进行数值模拟,详细探讨其内部的流场特性,研究流场内激波与边界层的相互作用。。通过分析间隙内的气体状态,建立反映流场本质特性的简化数学模型,定性分析流场特性,通过改变轴承流道结构,达到提高轴承承载力的目的。主要研究工作如下：①建立充分考虑惯性项、粘性项以及激波影响的整场数学模型,引入粘温方程,加入温度对粘性系数的影响。使用CFD软件采用层流模式对较小间隙下的轴承流场进行了较为准确的模拟。对较大间隙轴承流场,采用区域分解算法,将包括进气孔在内的轴承流场分为层流和湍流两部分,研究随着气膜厚度和供气压力的增加,斜激波与边界层的相互作用,气膜边界层的形态,以及气膜中斜激波结构的变化。②以单进气孔平面气体轴承为研究对象,对进气孔附近流速较快的情况采用量纲分析的方法推导了能量方程,获得了温度和马赫数之间的关系式。建立包含惯性力影响的静压气体轴承的控制方程,采用压力修正算法计算随着供气压力和气膜厚度变化,粘性力和惯性力的变化趋势,及其对压力分布的影响。结果表明,随着供气压力和气膜厚度的增加,惯性力增强,压力下降幅度增大。③根据间隙内气体流动的不同状态,建立了包含进气孔在内的超音速平面气体轴承分段流动模型,通过超音速状态下流量不变的条件,推导出超音速流场的压力、速度、马赫数和雷诺数简化公式,编制了计算程序,计算结果表明激波后的压力恢复最大值随供气压力的增大、气膜间隙减小、供气孔径增大而逐渐增大,为工程上预测压力与激波的关系提供理论参考。④在较高供气压力和较大气膜间隙下,提出合理大承载轴承结构,即适当增加喉口面积,调整通流面积的变化提高间隙内的压力。通过轴承结构的参数化设计及数值模拟仿真,获得了不同工况、结构、尺寸下的设计方法和原则,得出了流场性能变化规律。通过压力和承载力测试,验证了理论模型和数值计算方法的可靠性。更多还原

【Abstract】 In gas lubrication, the mechanical moving parts are supported by the gas film between clearances, the width of which is from several micrometers to several decade micrometers. Compared with rolling bearings and liquid lubrication bearings, the gas bearings possess merits:high speed, high precision, low friction, long lifetime and etc. However, the gas supply pressure, load capacity and gas film stiffness of traditional gas bearings are low to use within low load precise support. But the development of the sophisticated industry technology needs high load gas lubrication system urgently.The cause of low gas supply pressure in traditional gas bearing is that the velocity of gas between the clearances becomes supersonic from subsonic when increasing the gas supply pressure and the width of clearances. When the velocity becomes supersonic, the pressure will decrease steeply and will sometimes be below atmospheric pressure. Because of the complexity of flow process, the research on supersonic phenomenon in aerostatic bearings was generally based on one dimension simplified equations for a long period of time. With the interaction between shock wave and boundary layer, the result from the one dimension analysis on shock wave structures deviates, to a large extent, from the practice. So the further study on the mechanism of supersonic flow in the clearances under high gas supply pressure or big clearances is necessary, which establishes theoretical foundation for the development of high supply pressure, high load gas bearing.In this paper, the theoretic analysis, numerical calculation and experiment are combined with to conduct. Based on software Fluent, the exact flow field model was set up, the numerical simulations of the flow in the clearances were done; the flow characteristics and the interaction between shock wave and boundary layer were studied in detail. By analyzing the flow state of the gas in the clearances, the simplified mathematical model was set up which described the flow field essential properties; the essential flow field properties were qualitatively analyzed. The structure of gas bearings were improved, and the load capacity of them is improved. The main research works are shown as below:①The mathematical model of the whole flow field was built up considering the effects of inertia term and viscosity term, the viscosity-temperature equation was introduced to perfect its model. The laminar flow model in the CFD software was conducted to exactly simulate the flow field in the small clearances. For the flow field in the big clearances, the algorithm is qiute different in different regions of the flow field. The whole flow field including the gas supply hole is divided into two parts:laminar section and turbulent one. The interaction between oblique shock wave and boundary layer, property of gas film boundary layer and change of oblique shock wave structure were studied with the increase of gas film clearance and supply pressure.②The thrust gas bearing was chosed as a research subject, the dimensional analysis was conducted to derive the energy equation when the velocity near the gas supply hole was fast; the relation expression between temperature and Mach number was derived. The control equations considering the effect of initial force were set up; the pressure correction algorithm was used to calculate the change of viscosity force and initial force with both gas supply pressure and gas film clearance changing together. The effects of viscosity force and initial force on the pressure distribution in aerostatic bearings were studied as well. The result demonstrated that its inertial force stengthens and the pressure nearby the entrance drops more quickly with the increases of supply gas pressure and film thickness.③Based on the difference of the flow in clearances, the phase models were built up including the gas supply hole. The condition was introduced that the flow rate does not change under the supersonic flow, the simplified formula of pressure, velocity, Mach number and Reynold number were deduced and solved with self-defined programme, which provided theoretical reference for the prediction of the relationship between pressure and shock wave. The result showed that the maximum upswing pressure guadually increase with the increases of supply pressure and hole radius, and the decrease of film thickness.④The structure of gas bearing with high load capacity was designed under higher gas supply pressure or bigger gas film clearance working condition, that is, by increasing the area of its throat, the through-flow areas were modified to gain the pressure in the film. The simulation was conducted under different structure shape, different size and different working conditions; the method and principle of bearing design were achieved in different working states, and the change law of the flow field properties were derived as well. The test of static pressure and characteristics of bearings proved the reliability of the theory model and the calculation method.更多还原