Impacts of Part-to-Part Variability on Gas Turbine Blade Cooling
Open Access
- Author:
- Mc Cormack, Kelsey
- Graduate Program:
- Mechanical Engineering (MS)
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- September 28, 2023
- Committee Members:
- Robert Kunz, Professor in Charge/Director of Graduate Studies
Karen Ann Thole, Thesis Advisor/Co-Advisor
Reid A Berdanier, Committee Member - Keywords:
- Film cooling
Gas turbine heat transfer
Additive manufacturing
IR thermography - Abstract:
- Gas turbine inlet temperatures continue to increase in an effort to improve efficiency. Therefore, effective cooling of hot section components is necessary to reduce deterioration and maintain part life. Despite the best efforts of engine designers, coolant flow blockages or degradation of thermal barrier coatings will nevertheless occur during operation and lead to increased surface temperatures that reduce blade life. This phenomenon is especially prevalent in environments where sand or other small particles are ingested into engines. Part-to-part manufacturing variations also lead to significant changes in geometry relative to design intent that impact the flow and cooling effectiveness of turbine components, even when the deviations are within defined tolerances. This thesis examines part-to-part variations in geometry, flow, and cooling effectiveness for true scale turbine blades. A set of engine-run blades with varying levels of environmental deterioration was operated at engine-relevant conditions and surface temperature was measured using infrared thermography. These measurements were used to calculate cooling effectiveness and expected blade life. Blade flow parameter and cooling effectiveness were both high for blades operated in a benign environment, even though the benign run time blades had the highest run time of the blades measured. Blades operated in a harsh environment not only had lower cooling effectiveness, but also more variation in cooling effectiveness between blades. Film cooling trajectories were calculated for each set of blades tested, and showed that all engine-run blades had a significant reduction in maximum cooling effectiveness behind cooling holes with respect to a set of baseline blades. Cooling effectiveness values were then used to scale surface temperatures up to actual engine operating conditions extracted from the NASA E3 program. While lifing curves from previous literature were able to predict blade temperatures for benign environment blades, surface temperature increased much more than expected for harsh operator blades. A second study analyzed the flow performance and geometry of additively manufactured turbine blades with drilled film cooling holes. A benchtop flow rig was used to characterize flow through the full blade as well as isolated regions of the blade. While partial flow through specific regions of the blade did not match design intent, the total flow through the blade varied by less than 10% between the minimum and maximum flow blades at the design pressure ratio. Computed tomography scans were used to analyze the geometry of cooling features such as film cooling holes, crossover holes, turbulators, and pin fins. Shaped film cooling holes manufactured with a conventional electrical discharge machining (EDM) method were undersized throughout the entire cooling hole. A high-speed EDM method created holes that met design specifications in the metering section, but were also undersized at the hole exit. Additively manufactured features such as turbulators and pin fins were close to design intent shape and size, with the largest variations occurring on downskin surfaces that were unsupported during the build. Roughness was high on both internal and external blade surfaces, particularly for regions with the thinnest walls. This study demonstrated the viability of applying additively manufacturing and advanced hole drill methods to study new turbine cooling technologies at an accelerated timeline and reduced cost.