Efficient Modelling of Blade Film Cooling in Gas Turbines

Abstract

One of the most effective ways to mitigate thermal fatigue in a high-pressure turbine’s blades is by cooling the blade from inside and outside via an intricate cooling system. The cooling flow passes from the blade interior through many small holes to form a cooling film on the blade surface. In the early blade design phases, the designers must accurately determine the location, the pattern, the distribution density, the shape, and the size of cooling holes to maximize the blade film cooling whilst maintaining the external aerodynamics. Hundreds of simulation cycles may be needed to reach an optimal design. In this work, a film-cooling model and associated workflow are proposed. The model implementation within Ansys-Fluent uses a virtual-boundary concept which does not require the explicit resolution of the holes. The benefit of this is its compatibility with existing turbomachinery solution methods, and the consistency with subsequent mesh refinement toward resolved hole geometry. The workflow will allow designers to dissociate the uncooled aerodynamic geometry and mesh from the hole/film-cooling design, during the early design iterations. For verification of this approach, results for a simplified single hole-setup on a flat plate are first presented. A typical gas turbine vane configuration is then used to demonstrate industrial application. The results from an aerodynamic mesh refinement study show good agreement with the resolved model. Flexibility within the workflow for changing the location, shape and properties of the holes is also demonstrated. This approach, therefore, represents a useful design tool where multiple hole pattern configurations could be quickly assessed.