| Aerostatic bearings have been successfully used in high-precision machine tools, high-precision measuring instruments, high-speed rotors and so on because of their advantages such as high-speed, high-precision, and small power dissipation. Now with the increases of rotating speed, several problems arise. On the one hand, the influence of the dynamic effect caused by high rotating speed on the characteristics of them becomes more prominent, the calculation based on Reynolds equation could no longer satisfy the calculation accuracy requirement. On the other hand, the nonlinear factors caused by high rotating speed makes the linear theory of rotor dynamics unable to satisfy the research requirement of high-speed gas bearing-rotor system.In this paper, the improvement of system stability for high-speed aerostatic bearing-rotor system is taken as the research purpose, the systematic and in-depth research on the calculation of aerostatic bearing flow, the analysis of aerostatic bearing characteristics, the coupled research of the gas bearing-rotor system's characteristics, the experiment of the system. The main research work includes:The applicability of different calculation methods on aerostatic bearings is analyzed. The thrust aerostatic bearings are chose as a subject, the finite difference method based on Reynolds equation and the finite volume method (FVM) based on N-S equations are both used. For FVM, the laminar model, the turbulent model and the mixture of them are used. The four types of calculation results are compared with experiment results and analyzed. The Reynolds equation and the turbulent model of FVM are not able to satisfy the calculation accuracy requirement. Based on the comparisons of calculation accuracy and efficiency, the laminar model of FVM is chose for the subsequent study. The boundary layer separation, change of the flow state from turbulent to laminar and increase of viscosity are used to explain the pressure recovery after the pressure depression in the flow field.The static and dynamic characteristics of radial aerostatic bearings of different structure under different working conditions are studied with the three-dimension calculation method. The three-dimension models of radial aerostatic bearings are built, the model is divided into different districts, the calculation grids are refined in some districts. The static girds combined with the rotating coordinate are used for dynamic calculation. The dynamic effect improves the main load capacity and the main stiffness under high-speed working conditions, and the greater the eccentricity, the more obvious dynamic effect pressure. With the increase of rotating speed, the main stiffness increases, the main damping decrease, and the changes of the cross stiffness and the cross damping depend on the eccentricity. With the increase of gas supply pressure, the main stiffness increases, the cross stiffness increases within the bigger eccentricity range, and the changes of the damping depends on the eccentricity and the rotating speed. Under high-speed and big eccentricity working conditions, the influence of dynamic effect on the orifice-compensated aerostatic beaings is greater than that on the orifice-restricted aerostatic beaings, the main stiffness and the cross damping of the orifice-compensated are bigger than them of the orifice-restricted, but the cross stiffness and the main damping of the orifice-compensated are smaller. With the increase of the number of gas supply holes, the main damping increases and the influence of installation types of bearings can be ignored. The tangential gas supply holes can improve the main damping and decrease the cross stiffness with a large gas consumption, which is helpful to the system stability.The interaction method of aerostatic bearing-rotor system based on the calculation results from CFD is proposed. The nonlinear function of load capacity with rotating speed and eccentricity is obtained through fitting the calculation results under different working conditions. The nonlinear function is used to couple with the rotor dynamic equation, which realizes the coupling between the accurate flow calculation and the rotor dynamic equation. The influence of the dynamic effect and the rotor displacement on the system is fully considered in this method. The results show the relation between the imbalance amount and the response multitude is nonlinear caused by the nonlinear gas film force.The high-speed bearing-rotor experiment system is built, the new types of aerostatic bearings with tangential nonuniform supply holes and radial nonuniform district supply pressure are designed, the bearing-rotor system with different structure aerostatic bearings are test under different working conditions. One non-contact load exerting method based on the principle of aerostatic beaing is proposed, which can exert dynamic or static load on high-speed rotors. The compassion between experiment and theoretical results shows the proposed fluid-solid interaction method has a high calculation accuracy. Compared with the radial gas supply holes, the tangential gas supply holes can reduce the amplitude of the rotor runout, which certifies the correctness of the theoretical analysis of dynamic characteristics. The new type of aerostatic bearings with tangential nonuniform supply holes can improve the system stability. The new type of aerostatic bearings with radial nonuniform district supply pressure can reduce the amplitude of the rotor runout near the first order critical speed, but after the speed the amplitude increases. Under experiment conditions, the exerted load will increase the vibration of the system, and increase the amplitude of the critical speed. For the aerostatic bearings with radial gas supply holes, the amplitude of the rotor runout near the first order critical speed can be reduced with the increase of supply pressure, but after the speed the amplitude increases. For the aerostatic bearings with radial gas supply holes, the increase of supply pressure can improve the system stability. |
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