Heat Release in Turbine Cooling I: Experimental and Computational Comparison of Three Geometries

The ultracompact combustor is a design that integrates a turbine vane into the combustor flow path. Because of the high fuel-to-air ratio and short combustor flowpath, a significant potential exists for unburned fuel to enter the turbine. The current study explores the interaction of cooling flow from typical cooling holes with this high-temperature fuel-rich freestream flow. This was supplemented with a Reynolds-averaged Navier-Stokes calculation using a simplified two-step propane-air reaction scheme to model the combustion process and study the underlying physics of mixing between film-cooling and cross-stream-flow-driving secondary combustion. Results from surface temperature and heat flux measurements demonstrate that reactions in the turbine-cooling film can result in substantial increases in wall temperature for a considerable distance downstream of the hole. This increase depends on hole geometry, blowing ratio, and fuel content of the combustor flow. Furthermore, the heat flux increase only occurs when air is used as the coolant, as oxygen is needed to feed secondary combustion for the unburned fuel exiting the combustor at high equivalence ratios. Failure to design for this effect could result in augmented heat flux caused by the cooling scheme, and turbine life could be degraded substantially.