Thermal Analysis and Durability Design Strategies for Gas Turbine Airfoils

Abstract

Aircraft propulsion engines, land-based power generation, and industrial machines have, as a primary component, the turbine as means to produce thrust or generate power. In the turbine section of the engine, airfoil components are subjected to extremely complex and damaging environments. The combination of high gas temperatures and pressures, strong gradients, abrupt geometry changes, viscous forces, rotational forces, and unsteady turbine vane/blade interactions, all combine to offer a formidable challenge in terms of turbine durability. Nevertheless, the ultimate goal is to maintain or even improve the highest level of turbine performance and simultaneously reduce the amount of cooling flow needed to achieve this end. As such, coolant flow is a penalty to the cycle and thermal efficiency. Cooling strategies are developed and presented to determine ways for coolant flow management. The main variables include film cooling configurations, and convective efficiency schemes to balance turbine airfoil thermal loads for target overall cooling effectiveness. The desired targets are determined by the turbine airfoil durability requirements of oxidation and fatigue on a local scale and for creep on the bulk scale. Emphasis is provided to the general modes of cooling including film cooling, impingement cooling, and convective cooling for different parts of the airfoil such as leading edge, mid-body, trailing edge, tip and endwalls. Convective cooling is presented in terms of fundamental cooling enhancements, such as turbulating trip strips and pedestals. Recent literature dealing with these topics is listed.

Film Cooling Modelling for Gas Turbine Nozzles and Blades: Validation and Application

“…with film coverage and convective efficiency in excess of 50% [11]. Simply stated, the peripheral airfoil circuits will pick-up heat by convection in a very effective manner and then eject from film openings with high coverage designs to further reduce the thermal load to the part.…”

“…Peripheral cooling circuits are basically an array of vortex generators, designed to produce sustained longitudinal vortices in the bulk flow and thereby promote a global mixing capability in the cooling channel [11]. In addition, the coolant can be ejected at many points around the surface of the airfoil.…”