Improving Tilting Pad Journal Bearing Predictions—Part I: Model Development and Impact of Rotor Excited Versus Bearing Excited Impedance Coefficients

The floating-bearing-test-rig concept was initially developed by Glienicke in 1966 and has since been used to test many tilting-pad journal bearings (TPJBs). The impedances measured during these tests have been compared to rotor/journal-perturbed impedance predictions. Since the inertial acceleration of a pad is different for bearing-perturbed and rotor-perturbed motions, the bearing's reaction force components for bearing-perturbed and journal-perturbed motions will also differ. An understanding of how bearing-perturbed and rotor-perturbed impedances differ is needed to assess the validity of past, present, and future comparisons between TPJB test data and predictions. A new TPJB perturbation model is developed including the effects of angular, radial, and transverse pad motion and changes in pad clearance due to pad bending compliance. Though all of these pad variables have previously been included in different analyses, there are no publications containing perturbations of all four variables. In addition, previous researchers have only perturbed the rotor, while both the bearing and rotor motions are perturbed in the present analysis. The applicability of comparing rotor-perturbed bearing impedance predictions to impedances measured on a bearing-perturbed test rig is assessed by comparing rotor-perturbed and bearing-perturbed impedance predictions for an example bearing.