Flow Visualization of Microscale Effusion and Transpiration Cooling on Semi-cylinder for Gas Turbine Cooling Application

Effusion and transpiration cooling can be an attractive method of air cooling for the next generation high-efficient gas turbine which has a very hot gas temperature over 1,600°C (TRIT). For higher effectiveness of air cooling for a gas turbine vane and blade, the air-cooled flow through effusion-holes and porous metal surface should not penetrate into the mainstream flow but still remain within the thermal boundary layer. The present visualization study examines flow behavior of microscale effusion and transpiration cooling on semi-cylinder. The secondary flow issued from the effusion-holes and porous metal surface is visualized by a smoke-tube method which consists of oil droplet generator, diode pumped solid state (DPSS) laser and highspeed imaging. The flow visualization of microscale effusion and transpiration cooling on semi-cylinder is characterized with various blowing ratios. It is found that the transpiration cooling consumes less coolant air than effusion cooling and has better cooling effectiveness based on the same flow rate of coolant air. Visual criteria can be provided to maintain the effusion and transpiration cooling on semi-cylinder for gas turbine cooling application. [This work was supported by the National Research Council of Science and Technology (NST) grant funded by the Ministry of Science and ICT, Korea (Grant No. KIMM-NK219B).]