Reynolds' equations of the slot and bearing clearances are obtained to calculate load carrying capability, stiffness and damping coefficients of slot restrictor air journal bearing system. Dimensionless critical mass of rotor supported by one bearing would be obtained by means of solving 2-DOFs equations of only translatory mode whirling motion. A new type of slot restrictor air journal bearing with non-uniform slot shape is proposed to increase dimensionless critical mass of air bearing system. Non-uniform slot shape results in non-uniform pressure distribution. This pressure distribution will change static and dynamic characteristics of the bearing system. The stability characteristics can be enhanced, and dimensionless critical mass of the bearing rotor system can become much larger, if the changed shape of the slot is suitable for high-speed rotation. Dimensionless critical mass of the new bearings-rotor system would be analyzed by the same numerical analysis method. Numerical analysis of bearing-rotor system with 4-DOFs supported by upper and lower slot restrictor bearings would be performed for comparisons with experimental results of this thesis. The locus of the two journal centers in upper and lower bearings is obtained at a given rotational speed using the Euler method. The bearing system is stable if the locus has converging or limit cycling motion. The bearing system is unstable if the locus has diverging cycling motion. The rotational speed of the rotor is determined to instability threshold speed of the bearing system when the locus of the rotor center has limit cycling motion.
Experimental test rig is designed and experiments are performed to confirm the validity of the results of the numerical analysis. Rotor is vertical and it is supported by upper and lower slot restrictor bearings. Instability threshold speed and whirling mode of bearing-rotor system are obtained experimentally. The validity of the 4-DOFs numerical analysis method is confirmed by comparisons with experimental results.
As a result of the numerical analysis and experiment, the new type of the slot restrictor air journal bearing is found to be much more stable than a conventional slot restrictor bearing.
