Research On Static And Dynamic Characteristics Of Bearing-rotor System Of Turbo-expander In Cryogenic System

Turbo-expander is the core component of large cryogenic systems.The stability operation of the turbo-expander determines the safety of the entire system.The gas bearing was used in turbo-expander to support the static and dynamic loads of the shaft.Gas bearings are use gas as lubricant.Thus,the bearing can use the same gas with the system to avoid contaminate.Gas-lubricating journal bearings have advantages of lower heat generation,less contamination,higher precision and higher rotating speed capacity by comparison with traditional oil bearings.However,because the gas has the inherent characteristics of compressibility and low viscidity,the hydrodynamic pressure applied to the gas film of the bearing may cause large vibration which often limits the range of the application of gas bearings.The relationship between the static characters of the bearing and the style of the grooves are established in this article,and the method to improve the static stiffness of the grooved bearing was proposed.The dynamic model of the bearing-rotor system with elastomer suspension was established,and the mothed of damping adjusted to improve the stability was proposed which significient to the practical engineering.And also the model of surface waviness of the bearing was built,the analysis of the surface waviness to the stability of the system is significient to the manufacturing.Based on the research above,we can conclude:(1)Etching some grooves on shaft or bearing is proved to be effective in improving the static and dynamic performance by experiments.In practical engineering,the two styles of grooves: spiral groove and ? groove were used.The effect of groove styles and geometric parameters on the performance parameters of hydrodynamic gas bearings is presented.And a novel style of the groove is designed which can effectively improve the static and dynamic performance.(3)Based on the small perturbed assumption,the perturbed Reynolds equation was deduced,and the partial derivative method was used to solve the dynamic coefficients.The influence of the structure parameters and operation parameters to the dynamic coefficients of the gas bearing were analyzed.The linear stability analysis method was used to analyze the influence of operating parameters on the stability.(3)In this article,the effects of elastomer suspension to the stability of the bearing-rotor system were analyzed.The lower stiffness and the damping exponent values can improve the stability of the system.(4)Also,the influences of surface manufacture error on the bearing to the stability of system were analyzed by using the nonlinear analysis method.The waves in circumferencial direction can improve the stability of the system,and the waves in axial direction is harm to the stability.