Validation Tests for a Gas Turbine Thin-Shell Duct

Abstract Gas turbine (GT) liners, transition ducts and exhaust diffusers are large thin-shell ducts bounded by two barrels often joined together by struts. GT ducts are typically supported on one side only and they are free to expand inside the gas turbine so to avoid thermal distresses. The thin shell structure as well as the isostatic constraints make the GT ducts typically characterized by multiple natural frequencies inside the operating speed range of the engine rotor. GT ducts are however in most cases damped structures able to prevent high cycles fatigue failures. Damping is provided by sliding features as insulation and bolted joints. This paper describes the validation campaign of a redesigned transition duct (TD). The TD in object connects the flow path of a gas generator turbine with the flow path of a power turbine. The new TD has been made more robust to dynamic loads, in particularly it has been equipped of a damper capable to operate at high temperature. TD validation has been performed in two steps. The first step has been the dynamic characterization of the damper, this also includes the estimation of the friction coefficient at damper sliding surfaces. The second step has been a full-scale validation of the TD; tests have been performed on new TD but also on old TD, this allowed to compare the dynamic behavior of current vs new design and therefore determine damper contribution.