This paper presents an experimental investigation of the aeromechanical stability behaviour of a modern transonic fan blisk under flutter conditions. The measurements are conducted at the newly commissioned Fan Rig Darmstadt. Using an advanced capacitive blade tip timing system complemented by strain gauges and wall pressure transducers, the structural behaviour is characterised in detail across a wide range of speed and loading conditions.The results reveal distinct first flap flutter being the stability limiting phenomenon across the whole speed range, exhibiting varying nodal diameters. Modal and nodal decomposition confirmed the vibration at a natural frequency as well as the formation of coherent inter-blade-phase-angles varying with the operating condition. The onset of self-excited vibrations with exponential amplitude growth rates is confirmed by the experimental estimation of time-dependent system damping becoming clearly negative while approaching the stability limit.The detailed characterisation of the structural behaviour under flutter conditions provides a comprehensive experimental reference for the validation of numerical aeroelastic prediction tools as well as upcoming back-to-back comparisons with blade design variants. Furthermore, the work presented and the possibilities that arise with the capabilities of this new test facility can enhance the physical understanding of fan flutter mechanisms and thereby support the development of more reliable design rules for future aero engines.
Kilian et al. (Thu,) studied this question.