The Effect of an Upstream Ramp on Cylindrical and Fan-Shaped Hole Film Cooling - Part I: Aerodynamic Results

The present companion papers report the results of an experimental investigation on possible beneficial effects of an upstream ramp on discrete hole film cooling. This analysis was carried out on a flat plate model. Two hole geometries have been considered: cylindrical and fan-shaped with conical expanded exit. To compare different cooling schemes, a combined aero-thermal analysis was performed. Tests have been carried out at low speed and low inlet turbulence intensity level, with blowing ratios varied in the range 0.3–1.0. The aerodynamic investigation has been performed through the measurements of discharge coefficients and detailed flow field measurements. Surveys were carried out by traversing a flattened Pitot tube. Additional turbulence measurements have been carried out by means of hot wire traverses. All this information, together with the adiabatic effectiveness results presented in Part II of this paper, allowed drawing a comprehensive picture of the complex aero-thermal flow field in the injection region. The upstream ramp provided a moderate improvement in the case of cylindrical holes, as it allows the coolant to diffuse someway, before interacting with the mainflow, but it produced also a significant increase of aerodynamic losses. The fan shaped hole geometry without the ramp resulted to be the best solution, as it provides a coolant injection with a good lateral spreading and a low turbulence level.