Application of a Heat Flux/Calorimeter-Based Method to Assess the Effect of Turbulence on Turbine Airfoil Heat Transfer

The accurate prediction of turbine airfoil metal temperatures remains one of the critical issues in the development of high efficiency engines. Free-stream and wake-generated turbulence plays a major role in the external heat transfer of the cooled airfoils. Turbulence simulation experimental methodology has been employed to provide external heat load similarity between the engine and the elevated temperature cascade rig conditions. The methodology is based on simulation of turbulence intensity to produce equal mainstream heat transfer effects at the stagnation region of the airfoil in both engine and cascade environments. A recently completed fill-scale hot cascade facility provides a realistic simulation of an actual engine in terms of gas-side and coolant-side heat transfer. Significant attention is paid to emulating the free-stream turbulence environment of an actual engine. Indirect measurements of free-stream turbulence are performed with a custom designed calorimetric probe and heat flux probe. Well established stagnation point heat transfer correlations are used to deduce the free-stream turbulence intensity. The cascade rig provides a detailed map of local cooling effectiveness along the airfoil, which can be controlled by varying gas-side and coolant-side convective heat transfer. Results of the experimental study demonstrate the practical benefits of this methodology for more accurate evaluation of the airfoil external heat transfer, particularly when a combustor system is redefined or an engine is uprated and the airfoil cooling system has to be modified.