Session: 12-11 Code Development

Paper Number: 80700

80700 - Efficient Modelling of Blade Film Cooling in Gas Turbines 

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 air is extracted from the compressor and channeled to the turbine section, where it passes from the blade interior through many small holes to form a cooling film on the blade surface.

In the early design phases, a balance must be achieved to get the external and internal aerodynamics correct while minimizing the amount of extracted air from the compressor and, at the same time, maintaining an acceptable surface temperature of the turbine blades. For this balance to be achieved, 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. Hundreds of simulation cycles may be needed to reach an optimal design.

The most comprehensive simulation approach is to resolve the cooling holes. While this approach is accurate, it remains computationally expensive, especially given the number of potential variations in the early design phase. In this work, a film-cooling model is proposed and discussed. Unlike the traditional mass-source term approaches, the current implementation within Ansys-CFD uses a virtual-boundary concept, where the flow discretization is equivalent to classical inflow or outflow discretization. The benefit of this implementation is its compatibility with existing turbomachinery solution methods, and the consistency with subsequent mesh refinement toward resolved hole geometry. This approach will allow designers to dissociate the uncooled aerodynamic geometry and mesh from the hole/film-cooling design, during the early design iterations. Designers can then repeatedly use the same aerodynamic meshes that do not resolve any holes, while independently applying and evaluating arbitrary hole cooling patterns, without significant loss of accuracy. In addition, the hole locations and hole-specific flow conditions can be read from an external ASCII file, which facilitates scripting and automation of the design cycles.

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 (GE Energy Efficient Engine) 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 has also been demonstrated. This cooling model and virtual-boundary approach, therefore, represents a useful design tool during the concept design phase, where multiple hole pattern configurations could be quickly assessed.

Presenting Author: Justin Penrose ANSYS UK

Presenting Author Biography: Justin gained his PhD in simulation and clinical engineering from the University of Sheffield, and joined ANSYS 20 years ago. For the last 10 or so years, he has worked within CFD solver development. This has involved specialising in a number of areas, including Fluid-Structure coupling, Radiation modelling, and free-surface simulation. Most recently he has worked within the Turbomachinery Methods Group, implementing generalised models for simulating mass injection at boundaries. He is based in the UK, living not far from Oxford with his family.

Authors:

Justin Penrose ANSYS UK
Laith Zori Ansys Inc
Juan Carlos Morales Ansys Inc
Sunil Patil Ansys Inc
David Pons Ansys Inc
Samir Rida Ansys Inc