粗糙表面微型气体轴承润滑性能及其转子动力学特性研究

Surface roughness effects on gas journal microbearing performance and rotordynamic system in microfluidic applications

微型气体轴承-转子系统作为微型旋转机械实现功能转换的重要部件,表面粗糙形貌、薄膜润滑性能及转子动力学特性是影响整体设备可靠运转的关键因素.利用Boltzmann稀薄效应模型修正可压缩气体动压润滑Reynolds方程,通过分形理论表征微型轴承表面的粗糙轮廓,研究了气体稀薄效应和表面粗糙度耦合作用下微型轴承的静动态性能.并利用有限元法建立粗糙表面微型气体轴承-转子系统的动力学模型,得到转子系统固有特性和轴心轨迹的变化规律.结果表明:表面粗糙度效应提高了轴承的承载能力和动态刚度系数,在较大轴承数时增加幅度更明显.由于稀薄效应降低了轴承的直接刚度系数,转子振幅随气膜稀薄程度的增加而增大,表面粗糙峰的增加会降低转子系统的固有频率.

The aerodynamic lubrication performance of journal microbearing and the rotordynamics of microbearing-rotor system are of great importance to the stability of micro rotating machinery for realizing function conversion.The surface roughness,thin film lubrication problem and rotordynamics are the key factors affecting the safe operation of various microfluidic devices.Based on the Duwensee′s slip correction model and the fractal geometry theory,the interactive effects of gas rarefaction and surface roughness on the static and dynamic characteristics were investigated under various operation conditions and structure parameters.The modified Reynolds equation,which governs the gas film pressure distribution in rough bearing,is solved by employing the partial derivative method.The dynamic model of gas microbearing-rotor system is established by finite element method,and the variety of the natural frequencies and axes trajectories are obtained.The results show that high values of the eccentricity ratio and bearing number tend to increase the principal stiffness coefficients significantly,and the fractal roughness surface considerably affects the ultra-thin film damping characteristics compared to smooth surface bearing.Because the rarefaction effect decreases the direct stiffness coefficients of gas microbearing,the vibration amplitude of the rotor increases with increasing rarefied content of gas,and the increase of the roughness heights will reduce the natural frequency of rotor system.