Thermal Characteristic Analysis And Rotordynamic Experimental Study Of Aerostatic Porous Journal Bearings

The inner surface of porous gas bearing evenly distributes a lot of orifices,and each orifice plays a role in the throttle.Porous gas bearings have higher bearing capacity and higher rotation accuracy compared with other types of aerostatic bearings.Moreover porous gas bearings have high temperature resistance and corrosion resistance.Porous bearing has wide application prospect in the area that needs high bearing capacity and stability.With the development of high precision machine industry,porous aerostatic bearings also have been widely used in precision machine tools and high precision measuring equipment.On the basis of previous studies,the temperature characteristics of the porous bearings was studied.And the rotordynamic response of a rotor supported on porous gas bearings was conducted.The main research contents of the dissertation are as follows:Because of the compressibility of air,porous gas bearings are prone to cause pneumatic hammer instability.To avoid this instability,a surface-restricted layer that has smaller permeability than the bulk of the porous material is formed on the bearing surface.In this thesis,a theoretical study on the porous aerostatic bearing with a surface-restricted layer was presented.A theoretical model for predicting the temperature of porous aerostatic bearing with a surface-restricted layer was proposed by coupling gas flow equations,energy conservation equations,heat conduction equations and thermal expansion equations in the three-dimensional coordinate system.The temperature distribution of porous bearing under different rotating speed and different load conditions were analyzed.The influence of bearing clearance and hollow shaft thickness on the bearing temperature characteristics,maximum film temperature,maximum film pressure and minimum film thickness of the bearing were studied.Both the results that considering and neglecting the thermal expansion were compared.This study provides a theoretical basis for the design and application of porous bearings.A test rig for the rotordynamic tests of the porous gas bearing system was built.The dynamic balancing test of the test rig rotor was carried out by using the method of influence vector.Slow roll compensation was adopted in processing the data.The imbalance of the rotor is greatly reduced,preparing for the experimental study of rotordynamic response.The volume flow of the two porous bearings was measured.The influence of the bearing supply pressure and the rotor assembling was analyzed.The permeability of the two porous bearings were predicted based on the measured volume flow.The tests of imbalance response was carried out on the test rig.By recording and analyzing the displacement and keyphaser signals,the rotor responses for different bearing supply pressures and imbalances were analyzed.The rotor modes under different test conditions were analyzed.Both the horizontal and vertical synchronous responses at the disc and turbine ends were analyzed and compared under bearing supply pressure of 0.50 MPa.