Session: 12-01 Turbine Film Cooling

Paper Number: 80377

80377 - Influence of Porosity on Double-Walled Effusion-Cooled Systems for Gas Turbine Blades 

Double wall cooling systems for gas turbine blades utilise two skins connected by pedestals and take advantage of cooling through impingement jets and film holes. The latter exhaust coolant externally onto the blade surface forming a protective layer against the high external heat loads. This can be made more effective by taking advantage of the beneficial influence of the proximity of adjacent films. Consequently, increasingly porous outerskins are considered to provide greater thermal protection or reduce the required coolant mass consumption. To realise such systems, further research must understand how the internal aerothermal field is affected by high porous outerskins. A semi-decoupled unitblock computational fluid dynamics (CFD) method is applied to a range of geometries to understand overall cooling effectiveness as well as internal cooling and flow characteristics. A comparison of internal convection highlights the shift in the breakdown of cooling performance, due to the large changes in wetted surface area of the outerskin. For low porosity, most of the internal cooling occurs through the jet impingement and lateral jet on the internal outerskin wall, and as more film holes are added, internal cooling shifts toward the film hole walls. Externally, porosity increased film effectiveness due to the influence of film superposition, provided a more uniform film coverage, and reduced the likelihood of jet-lift-off. Coupling of internal cooling and film effectiveness benefits resulted in a reduction to mean metal temperature as well as peak temperature, as well as a reduction of the temperature gradient between the outer and inner walls. These three criteria reflect a reduction in the main drivers for thermal fatigue. Despite the benefits, variation in mass flow between film holes was observed, and in some cases the risk of hot gas ingestion was evident, but these can be minimised through considered design.  

Presenting Author: Matthew Courtis Oxford Thermofluids Institute

Presenting Author Biography: Matthew Courtis is a PhD student at the Oxford Thermofluids Institute studying advanced jet engine cooling systems under supervision of Prof Peter Ireland. This work is in collaboration with Rolls Royce Plc and explores double-skinned effusion systems and the progression toward transpiration cooling for enhanced thermal protection of critical turbine blade components. He earned his MRes in Gas Turbine Aerodynamics at the University of Cambridge and MEng at the University of Oxford.

Authors:

Matthew Courtis Oxford Thermofluids Institute
Peter Ireland Oxford Thermofluids Institute