Experimental characterization of particulate deposition on turbine vane leading-edge models with various showerhead cooling geometries

Designing film cooling for the leading-edge area of a turbine vane is much challenging due to the highest thermal load, flow stagnation, as well as distorted incoming flows. Contaminant particulate matters contained in the intake air and from the combustion production extremely complicate the matter by depositing on the surface. The build-up of the deposits roughens the surface and clogs film holes, increasing heat transfer rates and deteriorating film cooling performance. This study thereby has an attempt to evaluate the effects of showerhead cooling geometries on deposition patterns and thickness, as well as changes of film injection behavior and flow losses caused by deposition. Deposition on a generic leading-edge model with five rows of film holes, which were scaled up from an actual turbine vane, was experimentally simulated in a low-temperature wind tunnel using atomized wax particles. Deposition evolution was examined for various coolant flow rates. Specifically, the effects of showerhead cooling, which featured distinct injection and pitch angles and various row layouts, on deposition were investigated to explore deposition-resistance cooling structures for vane leading-edge areas. Deposition patterns and thickness were inspected using an optical scanning device and the film injection behaviors were visualized through a schlieren photography system. Further, the resulting flow losses through the film holes were quantified by measuring discharge coefficients. The thickest deposits were spotted near the flow stagnation, regardless of the coolant injection rates and the showerhead cooling geometries. Film injection was found to prevent from deposition by blowing off and cooling down the particles. Additionally, denser, staggered hole rows yielded less deposition and steeper, bidirectional injection was favorable to reducing deposition as well. As a result, the lowest capture efficiency of 5.3 % was found for the cooling configuration with an injection angle of 30° and a pitch angle of 15°. Though deposition induced flow losses and thus lowered discharge coefficients, the presence of deposition was able to redistribute coolant among the hole rows, allowing for more coolant issued from the upstream rows. The sparsest hole row geometry suffered the most deposition, whereas it possessed the highest discharge coefficient both before and after deposition, resulting in the lowest reduction of 14.3 % in discharge coefficient by deposition.