Blade Turbines transpiration

Behning, F.P., Schum, El.J., and Szanca, E.M., Cold-Air Investigation of a Turbine with Transpiration-Cooled Stator Blades, IV—Stage Performance with Wire-Mesh Shell Blading, NASA, TM X-2176, 1971. 

Temperature limits of flight engine alloys have been steadily inereasing about 20 °F (11 °C) per year sinee 1945. Transpiration and internally eooled metal blades have resulted in higher temperatures and more effieient operation. But the direet eorrelation between effieieney and fabrieation eost has resulted in a situation of diminishing returns for the superalloys. As more and more eooling air is needed for the superalloy eomponents, the effieieney of the engine drops to a point where turbine inlet temperatures around 2300 °F (1260 °C) are the optimum and, at that point, they are uneeonomie for automotive use. 

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