Effect of Blockages on Film Effectiveness on the Pressure Surface of a Turbine Blade

Abstract

An experimental and numerical study was conducted on fan-shaped holes on the pressure surface of a high-pressure turbine blade. Blockages in these film holes can arise through dirt accumulation as well as erosion of the thermal barrier coatings. The objective was to study the effects of partial blockages on film cooling effectiveness. Similar studies have been conducted on flat surfaces. This study includes the effect of curvature, which has been shown to be influential on film cooling performance. A blade with a single row of nominal fan-shaped holes at a lateral inclination of 30 deg was tested and used as the baseline performance. Blockage cases were then tested at various blowing ratios, with partial blockages in the throat as well as partial lidding in the fan exit of the film hole. The experiments were carried out using pressure-sensitive paint (PSP) in the high-velocity 2D linear cascade experimental facility at the Oxford Thermofluids Institute, using engine-representative Mach and Reynolds numbers. The results show that lidding with up to 0.5 blocking ratio (defined as the ratio of lidded length to the length of the film hole exit, in the film hole plane) only has a minor impact on film effectiveness, while lidding with 0.75 blocking ratio as well as throat blockage both result in significant deterioration of film cooling effectiveness. The effect of blockages on the discharge coefficient was also studied, and only blockages in the throat were found to reduce the discharge coefficient.