On the assessment of CFD assumptions for the preliminary design of a two-stage high-pressure turbine: Impact of unsteady effects on thermal loads

This paper aims to evaluate the influence of numerical assumption in a Computational Fluid Dynamics (CFD) analysis for the preliminary design of gas turbines (GTs). In the early design phases steady state CFD analyses still represent a key tool for predicting GTs performance, thanks to the good balance between results accuracy and computational costs. However, unsteady analyses are known to be the only one capable of capturing the interaction between GT components properly, even if they come with a higher computational cost. This paper concentrates on the CFD approach used in the preliminary phase where flow path and airfoils are defined, while disk cavities, squealer tips, seals, cooling and other details are not yet in their final form and will be defined at a later design phase. The paper describes the geometry and operating conditions simplifications typically adopted in the early design phase and continues discussing aero-performance and thermal loads. The paper discusses also steady and unsteady approaches as the adoption of computationally efficient CFD tools permits early multistage unsteady calculations. Unsteady effects are shown to have a strong impact on both momentum and enthalpy mixing. Unsteadiness should be carefully considered in the design process to guarantee an accurate prediction of gas temperature distributions as well as aerodynamic load that control the airfoil thermal load and ultimately the robustness of cooling and purge system design. • A cooled 2-stage high-pressure turbine is analyzed with steady/unsteady simulations. • Unsteady approach is critical for predicting components thermal loads. • Radial mixing plays a key role in predicting temperature distributions. • Component durability may be significantly affected by thermal loads.