Why are turbine blades cooled and what is the primary cooling method?

• A. To withstand high turbine inlet temperatures; primary cooling uses external water spray.
• B. To withstand high turbine inlet temperatures; primary cooling uses internal air channels and film cooling at blade surface.
• C. To reduce weight; uses vacuum cooling.
• D. To air-condition the engine compartment.

Answer: (B)

Because turbine inlet temperatures are extremely high, turbine blades must be cooled to survive and to allow higher operating temperatures that improve efficiency. The primary cooling method uses bleed air from the compressor that is routed through internal hollow passages in the blade to remove heat, and part of that air is ejected through small holes to form a thin protective film on the blade surface (film cooling). This combination keeps the blade surface cooler than the surrounding hot gas while the blade core remains within material limits. External water spray cooling isn’t the standard method for blade cooling, and vacuum cooling or air-conditioning the engine compartment aren’t applicable to this purpose.