Secondary reactions of turbulent reacting flows over a film-cooled surface

Abstract

Demand for greater engine efficiency and thrust-to-weight ratio has driven the production of aircraft engines with higher core temperatures and pressures. Such engines operate at higher fuel–air ratios, resulting in the potential for significant heat release and chemical reactions on a film-cooled surface. Currently, there is little basis for understanding the effects on aero-performance and durability due to such secondary reactions. In this paper, the chemically reactive turbulent film cooling over a surface for three cases of an inclined single and two parallel and compound-angle coolant holes is investigated by a Reynolds-averaged Navier–Stokes approach with the shear-stress transport (SST) turbulence model using OpenFoam. To take into account the secondary combustion resulting from the unburned fuels in the crossflow, a two-step reaction scheme was used for the combustion of propane. The relative increase in surface heat flux due to near wall reactions was investigated for film cooling with N2 and air injections. An eddy dissipation concept fast chemistry approach was used to account for the turbulence–chemistry interaction. Results demonstrate that reactions in the turbine cooling film can result in increased heat transferred to the surface. Failure to design for this effect could result in augmented heat transfer caused by the cooling scheme, and turbine life could be degraded substantially. The analysis suggests that high fuel–air ratio designs may have to consider changes to cooling strategies to accommodate secondary combustion.