Adiabatic and Overall Effectiveness for the Showerhead Film Cooling of a Turbine Vane

There have been a number of previous studies of the adiabatic film effectiveness for the showerhead region of a turbine vane, but no previous studies of the overall cooling effectiveness. The overall cooling effectiveness is a measure of the external surface temperature relative to the mainstream temperature and the inlet coolant temperature, and consequently is a direct measure of how effectively the surface is cooled. This can be determined experimentally when the model is constructed so that the Biot number is similar to that of engine components, and the internal cooling is designed so that the ratio of the external to internal heat transfer coefficient is matched to that of the engine. In this study, the overall effectiveness was experimentally measured on a model turbine vane constructed of a material to match Bi for engine conditions. The model incorporated an internal impingement cooling configuration. The cooling design consisted of a showerhead composed of five rows of holes with one additional row on both pressure and suction sides of the vane. An identical model was also constructed out of low conductivity foam to measure adiabatic film effectiveness. Of particular interest in this study was to use the overall cooling effectiveness measurements to identify local hot spots which might lead to failure of the vane. Furthermore, the experimental measurements provided an important database for evaluation of computational fluid dynamics simulations of the conjugate heat transfer effects that occur in the showerhead region. Continuous improvement in both measures of performance was demonstrated with increasing momentum flux ratio.