THERMAL PERFORMANCE COMPARISONS OF ADVANCED COOLING DESIGNS UNDER ENGINE REPRESENTATIVE CONDITIONS

Novel turbine blade cooling geometries have conventionally been assessed using computational methods, simplified flat-plate geometries, or large-scale wind tunnel models all at low technology readiness levels. Even when cooling geometries have demonstrated a beneficial heat transfer augmentation in simplified test environments, additional challenges arise when these features are integrated into real turbine hardware. In particular, integrated features are subject to design constraints and corresponding manufacturing-driven limitations. This study integrated cooling designs, previously reported in the open literature using simplified laboratory testing, into a true-scale turbine blade to assess the overall cooling performance of each geometry. The turbine blades were manufactured using a traditional single-crystal casting approach with complex internal cooling features and laser ablated film-cooling holes. Four unique blade sets were manufactured to evaluate three cooling hole geometries (cylindrical, 7-7-7 diffused, and tripod anti-vortex); additional comparisons were also made between trailing edge designs incorporating an offset, densely-spaced diamond pedestal array relative to a baseline impingement slot-fed design. Both the tripod cooling holes and the densely-spaced pedestals are cooling technologies that represent aggressive designs and also manufacturing challenges. All four sets of blade designs were tested concurrently using a rainbow wheel configuration in the Steady Thermal Aero Research Turbine (START) Lab. Blade surface temperatures were measured using thermal imaging methods over a range of cooling flow rates while computed tomography scans provided insight to how manufacturing variations impacted the mass flow rate through each blade. Results indicated that the anti-vortex tripod holes offer the most lateral spreading due to the wide coverage of the tripod design when compared with the baseline 7-7-7 hole design. The diamond pedestal trailing edge section showed similar overall effectiveness to the baseline design albeit at a lower mass flow rate to achieve the same blade temperature.