Experiments of Transpiration Cooling Inspired Panel Cooling on a Turbine Blade Yeilding Film Effectiveness Levels Over 95%

Authors

Augustin Suleiman Wambersie - Oxford University
Ignacio Mayo - Rolls-Royce
Peter Ireland - Oxford University

Abstract

Transpiration cooling has long been heralded as the future of turbine blade cooling, yet little medium to high fidelity data actually exists of how it performs in engine representative conditions. In this paper, experimental film effectiveness data of a novel blade cooling approach is presented. The novel approach, consisting of a large panel array of small film holes, presents a discrete but simple manifestation of transpiration cooling on the outer blade surface without the need for more complicated open foam approaches. In terms of film cooling, the method has the benefit of maintaining a very low blowing ratio over a large area of the blade allowing for high mass flows of coolant to be fed into the boundary layer, reducing the effects of coolant blow off.Panels were tested at different locations around the blade, on both suction and pressure surfaces. Three different surface porosities were also tried. Geometrically scaled blades were tested in a high speed wind tunnel with engine representative Mach number distributions. The use of PSP for film effectiveness measurements allowed for a high spatial resolution, crucial for the proper analysis of the detailed cooling geometries.Experimental results showed that the approach can be very successful with high levels of film cooling effectiveness achieved using low mass flow rates. The films were also seen to remain intact with minimal decay along the entire blade surface, particularly along the suction surface. Increasing the surface porosity also proved to be an important parameter in the panel's performance. Additionally, staggering the film holes lead to significant positive interactions between individual films, resulting in much improved panel performance.Limitations of the approach were still apparent at very low mass flow rates where uniform spanwise distribution and flow ingestion remained an issue.Comparison to analytical models and flat plate data indicate that the porous panel approach has a significant advantage over existing film cooling approaches used on turbine blades indicating a potential breakthrough in turbine blade cooling technology.