# THE MODE LOCALIZATION PHENOMENON IN TURBINES BLADES

## Palavras-chave:

Turbines blades, Modal analysis, Mode localization, Geometric stiffness, Centrifugal forces## Resumo

We present a numerical study of vibration modes localization phenomenon in blades of

aeronautical turbines. This kind of equipment is an example of a class of structures called periodic, that

are composed of a sequence of a large number of nominally identical substructures, the blades

themselves, lightly coupled by their hub. In the case they are really equal, the vibration modes will

extend to the whole set of substructures. If, as is to be expected of real machinery, there are very small

differences between the dynamic characteristics of the blades (stiffness, mass etc.), the mode localization

phenomenon may occur.

For localized modes, energy may get to be restricted to very few or even a single one of the substructures,

the turbine blades. This unexpected behavior may lead to catastrophic failure of the affected part due to

excessive vibration amplitude or accelerated fatigue considerations.

Our work is carried out using matrix structural analysis and we consider real geometric characteristics

of jet turbine motors for a more accurate modelling. Geometric stiffness due to traction centrifugal forces

are also taken into account, as such turbines rotate at very high frequencies. A case study of a N2 turbine

of the CFM56 engine is presented.