HP turbine blades are generally cooled by which of the following methods?

Correct Answer: Option C — Compressed air entering the root and exiting the tip.

HP turbine blades are internally cooled by compressor discharge air entering through the root and exiting via the tip or trailing edge. This internal cooling flow creates a protective film or convective cooling effect, preventing the metal from exceeding its metallurgical limits when exposed to high-temperature combustion gases.