Charles Lawrence

An Efficient Algorithm for Blade Loss Simulations Using a High Fidelity Ball Bearing and Damper Model

This paper presents a novel approach for blade loss simulation of an aircraft gas turbine rotor mounted on rolling element bearings with squeeze film dampers. The modal truncation augmentation (MTA) method provides an efficient tool for modeling this large order system with localized nonlinearities in the ball bearings. The gas turbine engine, which is composed of the power turbine and gas generator rotors, is modeled with 38 lumped masses. A nonlinear angular contact bearing model is employed, which has ball and race degrees of freedom and uses a modified Hertzian contact force between the races and balls. This combines a dry contact force and an equivalent viscous damping force. Prediction of the maximum contact load and the corresponding stress on an elliptical contact area between the races and balls is made during the blade loss simulations. A finite-element based squeeze film damper (SFD), which determines the pressure profile of oil film and calculates damper forces for any type of whirl orbit, is developed, verified, and utilized in the simulations. The new approach is shown to provide efficient and accurate predictions of whirl amplitudes, maximum contact load and stress in the bearings, transmissibility, the maximum and minimum damper pressures and amount of unbalance force for incipient oil film cavitation.Copyright

In Operation Detection and Correction of Rotor Imbalance in Jet Engines Using Active Vibration Control

Jet Engines may experience severe vibration due to the sudden imbalance caused by blade failure. This research investigates employment of on board magnetic bearings or piezoelectric actuators to cancel these forces in flight. This operation requires identification of the source of the vibrations via an expert system, determination of the required phase angles and amplitudes for the correction forces, and application of the desired control signals to the magnetic bearings or piezo electric actuators. This paper will show the architecture of the software system, details of the control algorithm used for the sudden imbalance correction project described above, and the laboratory test results.