Introduction

The underplatform damper for gas turbines is mounted within adjacent blades. The contact between damper and blade platform is ensured by the centrifugal force.

The device performs sealing functions and effectively dampens, using three different physical principles, the vibrations caused by fluctuation of the gas that passes through the turbine blades. The different damping mechanisms allow to target vibration modes different in terms of mode shape and frequency.

Technical features

The damper is composed of a casing and an internal pendulum (sheet and mass). The casing can take different shapes (eg cylindrical or wedge-like).

It damps vibration through three different mechanisms:

• Friction (the casing slides on the blades’ platforms)
• It serves as a vibration absorber (thanks to the appropriate dimensioning of the pendulum)
• Impact (pendulum against casing).

Impact damping also acts as a safety mechanism for the flexible parts of the damper (pendulum).

Possible Applications

• Gas turbines for energy production;
• Gas turbines for aeroengine;
• Steam turbines.

Advantages

• More effective than classical rigid dampers in targeting high-frequency modes.
• Allows to decouple the dynamic design of different modes of vibration. In detail, friction damping covers the first bending modes of the blade, while the pendulum acting as a vibration absorber can be used to target modes characterized by low platform mobility.