Experimental investigation on transpiration cooling through additively manufactured porous media

Some of first studies about transpiration cooling date back to the half of last century, where advantages and challenges of this promising technology were highlighted. Due to the multitude of problems related to the manufacturing of porous structures, film cooling is currently the most common active cooling technique to enhance gas turbines performances, increasing turbine inlet temperatures. With the advent of Additive Manufacturing, porous structures can be obtained with particular internal geometries, setting specific process parameters, such as laser speed, hatching distance, laser power. Bleed air is brought via impingement through the pores to critical surfaces which need to be cooled down to preserve their structural integrity and component lifetime. The aim is to establish a comparison between film cooling and transpiration cooling downstream performances using dimensional analysis. Results show higher adiabatic cooling effectiveness for transpiration samples and performances steadily depreciate with increasing coolant-to-mainstream momentum. To correlate these results to flow behavior, a method for flow visualization using an infrared thermal camera and carbon dioxide as tracer has been successfully developed and applied to cylindrical and porous samples. Finally, hot wire anemometry has been used to correct blowing ratio for porous samples and establish a fair comparison between different cooling technologies.