Nonlinear Reduced Dynamic Model of Turbofan Engine for Investigation of Engine Structural Frame Vibrations After Fan Blade Out Event

Abstract

Abstract This paper proposes an approach to construct a nonlinear dynamic model of a whole turbofan engine using the static condensation technique. Nonlinear dynamic behavior of the engine is described by a matrix differential equation, where the right side of the equation represents unbalance load and contact loads between the blades and casings, low-pressure (LP) shaft and high-pressure shaft. Elements of the matrices are calculated by static condensation of three-dimensional finite element models of rotors, casings, engine mounts, and wing attachment system. On the basis of the proposed approach, a model of the entire engine was constructed. The model considered contact interactions as well as effects associated with both instantaneous application of the unbalance load and the passage of the LP rotor through the critical rotational speed during the deceleration phase. The model has a modular structure that allows for the easy replacement of individual components and analysis of the various engine structural frame options. The results of engine structural frame load calculations after a fan blade-out event and during deceleration of the rotors to windmill mode are presented in this paper. In addition, the influence of the flexibility of fan supports, blade wheel nonlinear radial stiffness, and slowdown rates of rotors on load magnitudes are analyzed.