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The unsteady aerodynamics and aerothermics of a first stage gas turbine bucket with thermal barrier coating (TBC) and internal cooling configuration were investigated by application of a three dimensional Navier-Stoke commercial turbomachinery oriented CFD-code. Convection and conduction were modeled for a super alloy blade with TBC. This work is the second part of the paper “Unsteady 3-d conjugated heat transfer simulation of a thermal barrier coated gas turbine bucket”, and includes the simulation of shut down cycle. The CFD simulations were configured with a mesh domain of nozzle and bucket inter-stage using real turbine parameter data as boundary condition (BC) at nozzle inlet. The BC’s were adjusted in accordance with standard start-up and shut-down diagram for a gas turbine from Takahashi work [3]. Additionally a parabolic turbine inlet temperature was set for main gas flow. The problem was launched in a minicluster of 8 HP Workstation. Reasonably good comparisons in the main flow parameters with the manufacturer data were obtained. The effects of blade TBC surface temperature changes during a start-up and shut-down cycle were simulated using the Spalart-Allmaras turbulence model. A TBC can be used either to reduce the need for blade cooling (by about 36%) increasing the turbine efficiency, while maintaining identical creep life of the substrate; and increase considerably the creep life of the blade while maintaining level of blade cooling (and therefore allowing the blade to operate at lower temperature for an identical turbine entry temperature).Copyright © 2008 by ASME

The unsteady aerodynamic and aero-thermal performance of a first stage gas turbine bucket with thermal barrier coating (TBC) and internal cooling configuration were investigated by application of a three dimensional Navier-Stokes commercial turbomachinery oriented CFD-code. Convection and conduction were modeled for a super alloy blade with TBC. The CFD simulations were configured with a mesh domain including the nozzle and bucket inter-stage in order to accurately predict the fluid parameters at inlet and outlet of bucket. Comparisons to the gas turbine manufacturer data have permitted to validate the flow conditions at the inlet of the rotor. The effects of blade TBC surface temperature changes during a start-up cycle were simulated by means of an unsteady simulation, with unsteady inlet/outlet boundary conditions specified according to test data. The calculations include not only the fluid but also the solving of conduction within the blade, allowing for a correct modeling of the large difference of thermal inertia between the fluid and solid. The role of thermal barrier coatings (TBC) is, as their name suggests, providing thermal insulation of the blade. A coating of about 100–400 μm can reduce the temperature by up to 200°C. A TBC can be used either to reduce the need for blade cooling (by about 36%) increasing the turbine efficiency, while maintaining identical creep life of the substrate; or to increase considerably the creep life of the blade while maintaining level of blade cooling (and therefore allowing the blade to operate at lower temperature for an identical turbine inlet temperature).Copyright © 2008 by ASME