INVESTIGATION OF A METHODOLOGY FOR DESCRIBING FAN BLADE FLUTTER LIMITATIONS INDUCED BY NON-LINEAR FRICTION AT BLADE ROOTS

Abstract

. Fan Blade Flutter is an aeroelastic instability which may occur during the operation of a jet engine, depending on the working conditions of the fan stage. It finds its origins in some various mechanisms, including the impact of the environment of the fan stage, which may play an important role in the stability limits due to acoustic effects. If not properly taken into account, flutter can lead to an anticipated ruin of the fan stage as the fluid keeps on giving energy to the structure. However, nonlinear phenomena may appear at some high vibratory amplitude of the blades, resulting in energy dissipation of the aeroelastic system. Blade roots friction is an example of such a case : by dry-friction dissipation at blade roots, a limitation of the vibratory amplitude may be reached, the so-called Limit Cycle Oscillations (LCO), within the unstable regions of the operating domain predicted with a usual linear structural modelling. By taking these nonlinear effects into account, it is then possible to define more precisely the stability limits of the fan stage. In this paper, we describe a methodology to predict LCO induced by blade roots friction, including acoustic effects on stability. First, assuming a linear behaviour of the structure