Rotordynamic analysis of asymmetric turbofan rotor due to fan blade-loss event with contact-impact rub loads

Abstract

Rotordynamic analysis of asymmetric turbofan rotor due to fan blade-loss event with contact-impact rub loads Loss of a blade from a running turbofan rotor introduces not only huge imbalance into the dynamical system rather it makes the entire rotor asymmetric as well. In a nonsymmetric rotor, the various terms of mass, gyroscopic and stiffness matrices also become timedependent. In this paper, all the dynamical equations include the effect of the rotary inertia and gyroscopic moments as a result of both shaft bending as well as staggered blades flexing in-and-out of the plane of the disk. The governing equations also account for internal material damping in the shaft and the external damping in the support bearing system. In addition to the unbalance load at the disk location, the shaft may also be subjected to a torque and axial forces. Here, the fan blades are modeled as pre-twisted thin shallow shells. They have coupled flexural-torsional motion in the lateral out-of-plane direction as well as extensional degrees-of-freedom in the longitudinal spanwise direction of the blade airfoil. The effect of blade tip rub forces being transmitted to the shaft are analyzed in terms of the dynamic stability of the rotor, especially during windmilling.1 Sunil K.Sinha GE Aviation, General Electric Company, Cincinnati, OH 45215, USA blade-loss event on an engine are of proprietary nature and are not currently available in public domain. Any experiment simulating blade-loss or tip-rub under controlled conditions [11] is not only extremely expensive, rather sometimes they involve serious risk to the safety of the rig and the test personnel as well. As such there is a scarcity of test data, to compare the results of any fan blade-out analytical model in the published literature. However there are ample information from the actual field events and their investigation reports [12], which provide the necessary evidence about the magnitude of the dynamic loads due to fan blade-loss under operating conditions of a turbofan engine.In the aftermath of blade-loss, the fan-disk rotating system starts moving off-center in the heavier side of the disk due to sudden large imbalance introduced on the rotor-shaft. This eccentric rotor no longer remains symmetric about its center of rotation, and the spinning of the asymmetric rotor introduces another set of nonlinearities. Recently an attempt has been made to analyze the free vibrational characteristics of a weakly asymmetric rotor [13]. The present work is the first paper of its kind in the field of rotormechanics which addresses the forced transient response of an asymmetric flexible bladed-rotor with also considering the casing rub-surface flexibility in its formulation while the outer fan-case is still effectively undeformed. The inner surface abradable flexibility is expressed by an equivalent term K Rub and its dynamic effect on the blade-tip is included using a penalty method approach.In this paper, we consider the transient dynamic response of a complete rotor system in a jet engine w...

Experimental and numerical simulation of a rotor/stator interaction event localized on a single blade within an industrial high-pressure compressor

“…As a counterpart, structural contacts between these components may occur more frequently and must now be accounted for as part of nor-mal engine running conditions in non-accidental configurations. Subsequent vibratory phenomena may involve a single blade-it is then usually referred to as rubbing [1][2][3]-a full bladed disk and the surrounding casing-with possible modal coincidence yielding very high amplitudes of vibration [4,5]or precessional shaft motions such as backward or forward whirl motions [6][7][8][9]. A usual strategy employed by engine manufacturers in order to mitigate such vibratory phenomena involves the deposition of an abradable coating along the casing contact surface [10,11].…”

Vibration of a mistuned three-bladed rotor under regular and chaotic excitations

“…Next, these are solved analytically or numerically to test the system stability, individual blades motion synchronisation etc. (Crespo da Silva, 1998; Chandiramani et al, 2002;Sinha, 2013).…”

Towards Full 3D Numerical Simulation of Whirl Motions Stemming From Unilateral Contact Constraints in Aircraft Engines

“…A third type of rotor/stator interactions due to structural contacts is related to the occurence of orbital motions of an aircraft engine fan stage around its axis of rotation. These whirl motions [9,10] may feature significant displacements of the center of the rotor thus considering a negligible impact of gyroscopic effects is not an acceptable assumption anymore. As a continuation of previous research work on whirl motions based on simplified 2D models [11], this contribution discusses the development of ROMs accounting for both centrifugal and gyroscopic effects over a wide angular speed range.…”

“…The simulation of whirl motions initiated by blade-tip/casing contacts is intrinsically non-linear and constitute a challenge from a numerical point of view. Such numerical investigations have been the focus of several research work carried out in collaboration with different manufacturers [12,10,11]. So far, and to the best of the author's knowledge, these motions have never been predicted with full 3D finite element models and there is currently no way to obtain information specific to the balde design with respect to these interactions.…”