On the Divergence Mechanisms Analysis of a Vibrating Blade subjected to Repetitive Rubs with an Abradable Coating

Aeronautical compressor fans currently operate with minimal blade-casing clearance. This therefore makes the occurrence of rub events very likely. Under specific circumstances, the blade undergoes excessive amplification of contact-induced oscillations, called hereafter divergence, which can be critical for the structural integrity of the engine. This paper proposes an investigation of the mechanisms responsible for the blade divergence. Experiments are conducted on a fully instrumented laboratory set-up, consisting of a single flat blade being moved towards a rotating cylinder to initiate interactions, while monitoring the vibrations and the evolution of wear on the abradable coating. Two synchronization mechanisms have been identified as facilitating the divergence: (i) the inherent set-up synchronization between the vibration modes related to the horizontal and vertical motion of the blade; (ii) the preferential blade-coating interactions in the vicinity of periodically distributed irregularities of the abradable coating which act as a source of excitation of the vibrations.