Impact of aerothermal modeling on the estimation of turbine blade life

Abstract

The impact of aerothermal modeling on estimates of turbine blade heat transfer and life was assessed for three high pressure turbine blades. The work was conducted as part of a project aimed at the evaluation of the effect of variability on turbine life. Pressure and thermal loads were extracted from numerical simulations, postprocessed, and used as external boundary conditions in thermal-structural calculations aimed at the estimation of blade life. Deterministic calculations of life showed that blade life differences of 17% and 34%, relative to the baseline blade, were primarily due to structural differences between the blades rather than differences in external aerodynamic and heat transfer characteristics. The simulation results for the three blade geometries were used to construct probabilistic external thermal boundary conditions with variability based on expected in-service variability for heat transfer coefficient and convection temperature. In a parallel study, these were used as noise parameters, along with metal and thermal barrier coating conductivity, thermal barrier coating thickness, internal cooling temperature, and internal heat transfer coefficient, in three probabilistic blade life calculations. Consistent with the deterministic findings, a weak to moderate correlation was found between the variability in external thermal conditions and that in blade life. The key driver of life variability was the variability in the internal cooling temperature. The impact of modeling approximations and geometric and flow features on blade life was also investigated on one of the nominal geometries. A set of two-dimensional numerical results were used to assess the impact of using simplified data in the estimation of life.

(cont.) Geometric and flow features considered in three-dimensional studies were a seal cavity between rotor and stator, seal cavity flow, fillet geometry, and inlet boundary layers with and without seal cavity. Despite differences in blade external heat transfer of 10% - 15% in the life-limiting region, the estimated life for all blades in these studies was within 2.6% of the nominal. For turbine blades of similar design and operating conditions, given our modeling approach, it was concluded that (1) the level of heat transfer differences observed between blade designs does not play an important role in the estimation of blade life and (2) high fidelity modeling of external aer.