Modal characteristics of turbine blade packets under lacing wire damage induced mistuning

Abstract

Effect of mistuning on turbo machine blade vibration in a packeted blade–disk system has become an important area of research in the recent past, mainly due to the critical applications in aero engines and power plant turbines. It has been shown that even a small mistuning can lead to stress build up through mode localization under forced vibration. Such mistuning can come from initial geometric blade to blade variation due to manufacturing tolerances or from a crack growing in the bladed disk system during operational life stages. The literature review indicates that researchers have mainly considered blade damage as a cause of mistuning. However, lacing wire damage, although not as catastrophic as blade damage, are more frequent in occurrences and often act as a precursor to subsequent blade damage. Detection of lacing wire damage is therefore equally important. Present work has investigated nature of mistuning induced by lacing wire damage and its effect on the characteristic modal properties. A damage severity index has been introduced and effect of damage on the blade group natural frequencies is investigated. Scope of developing a damage identification methodology in packeted blade–disk system is also discussed.