Test, and Mitigation of 1/2x Forward Whirl Following Rotor Drop Onto Auxiliary Bearings Simulation

Abstract 1/2 forward whirl repeatedly occurred after a test rotor spinning at 5800rpm was dropped onto ball bearing type auxiliary bearings (AB), utilized as a backup for magnetic bearings (MB). The measured contact forces that occurred between the rotor and the AB during the subsynchronous vibration were about thirteen times larger than the static reaction force. The vibration frequency coincided with the rotor-support system natural frequency with the rotor at rest on the AB, an occurred at of the rotor spin speed when dropped. The test rig provided measurements of rotor-bearing contact force, rotor orbit (vibrations), and rotational speed during rotor drop events. A simulation model was also developed and demonstrated that parametric excitation in the form of a Mathieu Hill model replicated the measured forward whirl vibrations. The simulation model included a nonlinear, elastic-thermal coupled, ball bearing type AB model. The transient model successfully predicted the vibration when the rotor was passing 5800 RPM as well, and the simulation results quantitatively agreed well with the test results in the frequency domain. Several approaches for mitigating the 1/2 forward whirl were presented such as adding an elastomer O-ring or waviness spring in the AB support system. Measurements confirmed that adding AB dampers effectively mitigated the subsynchronous forward whirl and significantly reduced the contact forces.

Simulation, Test, and Mitigation of 1/2x Forward Whirl Following Rotor Drop Onto Auxiliary Bearings Academic Article