Transient Vibratory Response of Turbofan Engine Rotor Impacted by Bird Strike

This paper presents a semiclosed-form physics-based rotordynamic analysis which determines the transient bird-strike load at the blade root and at the support bearings of a rotating fan shaft. This research considered a turbofan aeroengine application of a continuous fan shaft supported at multiple bearing locations and subjected to an impact loading caused by bird ingestion during normal flight operation of the aircraft. The mathematical formulation of the governing equation considers inertial effects as well as all circulatory terms involving gyroscopic and Coriolis forces. In the numerical simulation, the incoming bird was a cylindrical projectile and the blade was the target. The large impulsive load generated by the bird-strike incident traveled through the airfoil, fan disk, rotor shaft, rolling element bearings, and finally to the entire engine support structure. The structural details of the fan disk and shaft were treated as an overhung spinning beam supported on three bearings system. The highly nonlinear transient dynamic numerical results for all the relevant dynamical design parameters have been presented for a typical large commercial jet engine. It has been shown that the dynamic magnification factor for the transient vibratory response of the fan rotor impacted by a bird strike can be as much as 3 times that of the normal steady-state response of the similar unbalance.