CALCULATING COOLED TURBINE EFFICIENCY WITH WEIGHTED COOLING FLOW DISTRIBUTIONS

The ability to accurately characterize the thermal efficiency of turbine stages with cooled components is essential to advance turbine technologies. There are many methods for calculating aerodynamic efficiency of turbomachinery components, with most encompassing either single point or simple integrated values at the inlet and exit locations. For cooled turbine stages, there is an added complexity of how to incorporate cooling flow streams. Although these techniques may include multiple cooling flows, a fully-mixed assumption is often invoked without directly accounting for distributions of cooling flow in the annulus. However, the distribution of cooling flows in turbine stages may vary significantly depending on the location and nature of injection. This study addresses how calculated efficiency may vary depending upon how cooling flows are injected and the manner in which these cooling flows are accounted. The analyses utilize experimentally measured cooling flow concentration profiles to motivate a new approach for calculating cooled turbine efficiency with weighted cooling flow distributions. Validation data for a one-stage high-pressure turbine geometry from the Energy Efficient Engine (E-3) program are assessed to determine the range of influence for cooling flow distributions. Results show that cooling flows injected at similar axial positions can have unequal influences on integrated stage efficiency based on known distributions of cooling flow and other properties at the turbine stage exit plane. In some cases, deviations approaching half a point of efficiency can be observed relative to traditional equations, and the magnitude of influence is shown to increase as stage total pressure ratio decreases.