Modeling Film Cooling in Turbine Blade Design
Turbine designers have the challenging task of getting the external and internal blade aerodynamics right while minimizing the use of cooling air. They need to accurately determine the location, the density, the pattern, the shape and the size of cooling holes to maximize blade life. Hole placement must be optimized to minimize the negative impact on aerodynamic efficiency while maximizing cooling efficiency. This task takes place early in the airfoil design when detailed CAD models are either not yet available or the generation of detailed meshes with cooling orifices slows down the iterative design process significantly.
The designers want to separate the geometry (airfoil shape) from the mesh (typically hexahedral) and from the cooling flow distribution. They model a reduced number of passages for a single stage and make small changes to the airfoil without changing the hole position; conversely, they move the holes and change their sizes without modifying the airfoil geometry. This process is repeated for many airfoils and cooling holes configurations as part of an optimization loop. There are several approaches to account for cooling holes in CFD simulations which vary by order of complexity and the sought accuracy. These approaches are discussed in this white paper.