Film Cooling Hole Shape Effects on Turbine Blade Heat Transfer – Part II: Effects of Mass Flow Rate and Unsteadiness

To provide a detailed analysis of film cooling in a turbine environment, this study incorporates experimental and computational research performed on a rotating high pressure turbine stage. The turbine blades include rows of three different film cooling hole shapes investigated at several different cooling mass flow rates supplied to the rotor. Film cooling hole shapes include round, fan, and advanced anti-vortex shapes, and the performance of these cooling systems installed on the rotating blades are evaluated on time-averaged and unsteady bases. Film cooling hole shape and coolant mass flow provide different cooling benefits in different areas of the blade. Across the pressure surface, leading edge, and suction surface, advanced film cooling holes show the most response to changing coolant mass flow, and typically have the highest film effectiveness at the highest film cooling flow rate. Film cooling jets experience similar motions regardless of hole shape. Unsteady pressure gradients across the film cooling hole outlets on the pressure surface cause cooling jet motion. Fan and Advanced shaped holes cause lateral spread of cooling gas on a steady basis, and due to the increased lateral spread, a larger region on the pressure surface receives consistent film coverage. On a time-average basis, this results in much more lateral spread and increased film coverage for shaped film cooling holes. The results of this study help identify the performance of shaped film cooling holes in turbine environments. The response of different hole shapes to unsteadiness has a significant impact on the time average film cooling coverage. Additionally, the hole shapes respond differently to increased levels of coolant mass flow rate and provide different degrees of film cooling coverage on different parts of the blade. An increased understanding and appreciation of the unsteady performance of various film cooling geometries is a foundational piece of continued technology development.