Which of the following are primary methods for cooling turbine blades?

Cooling turbine blades is essential to maintain their performance and longevity under extreme operating conditions. The correct answer highlights two primary methods: cooling air and thermal barrier coatings.

Cooling air is injected into the blade, typically through internal passages, to lower the temperature of the blades during operation. This air absorbs heat from the blade material, helping to prevent overheating and ensuring that the blades remain within acceptable temperature limits.

Thermal barrier coatings, on the other hand, are specialized materials applied to the surface of turbine blades. These coatings act as insulators, reflecting heat away from the substrate material, which helps to protect the blade from high temperatures and oxidation. This combination of cooling air and thermal barrier coatings allows turbine blades to operate efficiently in high-temperature environments while extending their service life.

The other methods listed, while they may have some application in turbine systems, do not primarily serve the function of cooling turbine blades as effectively as the methods mentioned.