Analyzing Dynamic Rotor Instability on Gas Foil Bearings under High-Speed Electric Motor Testing

The rotational stability of a symmetrical rigid rotor with simultaneous whirling in gas-dynamic foil bearings is investigated on an analytical level. Velocity patterns are formulated with respect to the destabilizing effect of lubrication, which is much more significant for forward whirl mode of the rotor. When the rotor loses rotational stability and undergoes forward whirl, a case of self-oscillations is considered, accompanied by dry friction against the bearing leaves in the form of backward whirl. Here, it is established that the self-oscillation mode does not depend on imbalance. Therefore, all the results initially obtained upon the simplification that the rotor is balanced are valid when the rotor is unbalanced, too. It is shown that forced oscillations caused by imbalance, on the contrary, depend on self-oscillations. The applied potentialities of the developed method for analyzing such rotor systems are demonstrated.