Rotor-Bearing Analysis for Turbomachinery Single- and Dual-Rotor Systems

Finite element analysis models were developed to investigate the dynamic characteristics of single- and dual-rotor-bearing turbomachinery systems. When an inertial coordinate system was used, the dynamic models of the rotor-bearing systems included gyroscopic moments, rotary inertias, and bending and shear deformations. The models were analyzed to predict the natural frequencies, to produce critical speed maps, and to estimate the bearing stiffnesses. These rotor-bearing system analyses were then applied to both single-rotor and dual-rotor system applications. In the single-rotor system application, a small turbojet engine and its rotor components were used as a basis for the model. Both theoretical and experimental analyses were used to study this engine rotor-bearing system. Modal testing and a dynamic engine test were used to verify the analytical results, including the predicted critical speed map and the bearing stiffnesses. Very good agreement was found between the analyses and the test data. In the dual-rotor application, the effects of the speed ratio of the high-speed to low-speed shafts of the dual-rotor system on the critical speeds was studied. It was demonstrated that this speed ratio could be used as one of the dual-rotor system design parameters. Finally, it was noted that the interrotor bearing stiffness between the high-speed and the low-speed shafts of the dual-rotor system affected the mode shapes of the shafts within the system, in addition to the rotor system critical speeds.