58919 - Design and Validation of a New Damper 

Gas turbine (GT) transition ducts as well as exhaust diffusers are large thin-shell structures with multiple natural frequencies inside the rotor speed operating range of the engines. In most applications, GT ducts are supported on one side only and therefore they are free to expand inside the gas turbine colder casings, axially but also radially so to avoid thermal distresses.

The GT ducts are typically damped structures able to prevent high cycles fatigue failures. Damping is provided by sliding features as insulation or bolted joints.

The paper describes the redesign of the transition duct (TD) of the PGT25 engine after it was discovered that in some operating conditions it was cracking for HCF. The TD of the PGT25 connects the flow path of the LM2500 high pressure turbine with the flow path of the PGT25 power turbine.

The new TD has been made more robust, but it has also been equipped of dampers capable to operate at high temperature.

After a deep investigation of the TD modes that could be excited by flow path and/or by rotor vibrations, it was decided to add two dampers, one for each barrel of the TD.

Due to internal space limitations, a new type of damper has been designed for the external barrel.

Both dampers have been sized using FEA. Harmonic analyses including the dampers contribution have been performed.

Damper lab tests and TD validation tests have also been performed.