To prevent overheating of the illustrated turbine blade, which of the following fluids is circulated through it via the shaped internal passages? See Illustration GT-0035 Illustration GT-0035: the U.S. Coast Guard has not released this illustration.

Correct Answer: Option D — Bleed air.

High-pressure bleed air, extracted from the compressor section, is directed through internal cooling passages in turbine blades. This film cooling technique creates a protective boundary layer, preventing the metal from exceeding its metallurgical temperature limits when exposed to the extreme heat of the combustion gas path.