STRATEGIES FOR HIGH-ACCURACY MEASUREMENTS OF STAGE EFFICIENCY FOR A COOLED TURBINE

Gas turbines are used in a broad range of aerospace and land-based applications from power generation to aviation, and their usage is projected to continue to grow. As a result, it is critical to find innovative solutions for improving turbine efficiency to reduce fuel consumption and carbon emissions. Successful demonstration of new efficiency-increasing technologies at rig or engine scale requires efficiency measurement techniques that are both accurate and repeatable. The Steady Thermal Aero Research Turbine (START) Laboratory at the Pennsylvania State University is utilizing a unique 360° traversing system for temperature and pressure probes with redundant torque measurements to quantify thermal efficiency for a single-stage cooled test turbine. The purpose of this study is to determine a measurement method that produces highly accurate and repeatable efficiency calculations. With these systems, flows in the full annulus have been analyzed and compared with subsector traverse segments centered at different circumferential positions to determine the appropriate sector size. The results from this investigation indicate that the full 360° measurement is recommended to minimize variation in calculated stage efficiencies. This study also compares the circumferential variations in thermodynamic and mechanical efficiency calculation methods, finding that the thermodynamic efficiency calculation results in a higher accuracy for full exit plane measurements. In parallel, a statistical analysis was performed to determine the number of required repeats for the full 360° traverse necessary to achieve a desired precision uncertainty that is half of the bias uncertainty. Ultimately, this study establishes guidelines to streamline experimental procedures by limiting the necessary test count per operating condition to 10 measurements. Following these procedures establishes a bias of ϵ_b = 0.18 points, and limits the precision uncertainty to at most ϵ_p = 0.09 points, resulting in a total uncertainty of at most ϵ_t = 0.20 points.