An Insight Into the Snubbing Mechanism for the Reduction of Turbine Blade Vibration by Analyzing Chaotic Behaviour

Blade failure due to the overcoming of fatigue limit in turbo machinery for power generation could be fostered by excessive vibration level of the blade itself. Thus, blade vibration reduction is an important task, in order to avoid this risk, and can be achieved in different ways. One of these is a contact related phenomenon, which consists in physically limiting the vibration amplitude on the blade tip leaving a small gap between the shrouds of adjacent blades. When the relative displacement between adjacent blades exceeds the gap, in a certain vibration mode of the bladed disk, a contact occurs between the shrouds, the relative motion is restricted and energy is dissipated by friction and impact during the contact. This is the so called snubbing mechanism. In this paper, the relationship between vibration reduction due to the snubbing mechanism and chaotic behaviour onset is investigated numerically, by using a simplified, multi-degrees of freedom, model that has been already tested and experimentally validated for bladed disks. The level of vibration reduction is evaluated in some different cases and typical chaos measurement indexes are used.