Research Of Dynamic Characteristics For High Speed Hybrid Gas Bearing Rotor System

As the increasing of power density for power machinery, the rotor needs to work on high rotating speed. The bearing is the key component for limiting the high speed operation of rotor. The widely used rolling element bearing wears heavily and effects the life as the rotating speed is big, which generate from the contact between the components. For the liquid bearing, the friction waste power is large and the instability speed is low. So that two kinds of bearings are limited in the high speed application. The gas bearing can overcome the disadvantages of liquid bearing and rolling element bearing, which generates from that the low viscosty of lubricated medium for gas bearing. So the gas bearing is more and more widely employed in high speed rotating machinery. The hybrid gas bearing can avoid the bearing bush contact problem of aerodynamic gas bearing at lower rotating speed and increase the load capacity and stability, which become the high light of the research on gas bearing.The high speed hybrid gas bearing is studied as the research object in this dissertation. The static and dynamic characteristics of bearing are studied. By employing numerical and experimental method, the coupling dynamics of high speed hybrid gas bearing rotor system is studied by combining with nonlinear dynamic therotical and method. This offers the reference basis and effective therotical method for the rotor bearing system design of high speed rotating machinery.For the case that the aerodynamic performance and the aerostatic performance is calculated separately and then superimposed together in the classical hybrid gas bearing design, which ignore the couping effect, the compressible gas lubricated Reynolds equation including the small orifices flow term is established. The coupling solving of aerostatic and aerodynamic parameter for hybrid bearing is carried out by Newton method and finite difference method. To improve the bearing load capacity of gas bearing, the membrane restrictor gas bearing structure is proposed, and then the gas dynamic equation to describe the gas flow in membrane restrictor is established. That equation is couplingly solved with the gas lubricated Reynolds equation by fluid resistance method.For the stiffness and damping coefficients with whirling of the rotor in gas lubricated Reynolds equation is complicated to get, the average and modified parameters are acquired by employing the pressure distribution of multi-orifices aerostatic journal bearing. And the relation between the inlet and outlet pressure for orifice is obtained. The flow in the journal gas bearing is described by the transfer function, and the analytical form of nonlinear unsteady gas film forces for multi- orifices hybrid gas bearing is derived. By employing the Laplace transform the dynamic coefficients are acquired.For the case that usually the pressure and displacement derived with time is ingored in the research of gas bearing rotor system, the alternating direction implicit method is employed to calculate the transient flow field of gas bearing clearance, and then solved coupling with equations of motion for elastic rotor; For the case that in the coupling solving procedure, the gas lubricated transient Reynolds equation and equation of motion for rotor can not be solved simultaneously, the linear forecast multi-field algorithm is proposed. The nonlinear dynamics characteristics for gas bearing rotor system are studied. It indicates that the linear forecast multi-field algorithm can eliminate the hysteresis error caused by weak coupling algorithm and improve the efficient of calculation.Based on the characteristic of linear forecast multi-field coupling solving method, the corrospending harmonic excited dynamic characteristic coefficients identification method is presented. By considering effect of the excited frequency on dynamic characteristic, the dynamic coefficients coupling with the elastic deformation of rotor is acquired.Because the inner flow of rotating ramjet is sensitive to the geometry of structure, the internal flow in the rotating ramcompressor as whirling is studied, and then nonlinear coupling excited force model acting on the rotor is obtained. The gas lubricated Reynold equation including time terms is coupling solved with the motion of rotor, and the nonlinear rotor dynamic characteristics of hybrid gas journal bering-high speed rotor system with rotating ramcompressor complicated excited forces are obtained.The dynamic characteristics experiment of rotor bearing system is carried out on the high speed gas bearing-rotating ramjet experimental test rig. By comparing with the numerical results, the low frequency component in the experimental speeds and the distribution of statics balancing position are checked, which proves the correctness of coupling solving modeling and research method qualitatively.