Transpiration cooling of high pressure turbine vane with optimized porosity distribution

Abstract

The additive manufacturing allows to fabricate porous structures with elevated mechanical strength, which enable designers to apply transpiration cooling to gas turbine blades. However, most transpiration cooling investigations are carried out using the flat plate geometry. To understand transpiration cooling of a turbine blade better, it is necessary to conduct the investigations using real turbine blade geometry. The current study focuses on the numerical investigation and optimization of a transpiration cooled C3X vane. The C3X vane is designed with multiple porous zones whose porosities are in a range from 0.2 to 0.7. The Darcy-Brinkman-Forchheimer equation and the local thermal equilibrium model are used to simulate the flow and heat transfer in the porous zones. A surrogate-based optimization framework incorporating the Kriging method and the genetic algorithm is built to optimize the transpiration cooling performance. The numerical approach is carefully validated with the available experimental data, and then the optimization method is validated with the numerical results. The optimal designs under injection ratios of 1.2% and 2.0% are obtained, and the underlying flow structure and heat transfer physics are revealed. The results show that for an optimal transpiration cooled turbine vane design, large porosity should be applied first to the leading edge and the pressure side just downstream of the leading edge. The coolant issuing from the leading edge and the upstream pressure side convects downstream, forming an effective transpiration cooling film. The transpiration cooling film adheres well to the pressure surface, while it decays quickly on the suction surface. The temperature non-uniformity of the coolant in the plenum and the suction side endwall vortices can lead to the non-uniform surface temperature distribution along the vane height.