EXPERIMENTAL-VERIFICATION OF SUBCRITICAL WHIRL BIFURCATION OF A ROTORSUPPORTED ON A FLUID FILM BEARING

The paper presents the results of the experiments that were conducted on a short fluid film bearing with a simple single disk rotor.; The be havior of the journal was analyzed as a function of the rotor system p arameters such as the load, speed, and imbalance mass. It was verified that the journal bearing can.lose stability through either a subcriti cal or a supercritical bifurcation. In the supercritical bifurcation, the expected gradual increase in the amplitude of the limit cycle was observed, while in the subcritical bifurcation there was a sudden jump to a large limit cycle. In the case of a subcritical bifurcation, it was also observed that the journal bearing became unstable below the r otor threshold speed of instability;following a small perturbation app lied to the rotor Demarcations were made for the stable regions of ope ration (regions where the rotor is stable below the threshold speed of instability) for the journal bearing based an the obtained experiment al results. Experiments were also performed to analyze the effects of imbalance of the rotor on the threshold speed of instability. It was o bserved that the flexible unbalanced rotor had a lower threshold speed of instability. The limitations of the linear theory of fluid film be arings in predicting these phenomena are discussed.