How is thermal stress relieved on a turbine disc?

Thermal stress relief on a turbine disc is primarily achieved by directing bleed air onto the face of the disk. This method utilizes high-temperature bleed air, often taken from the engine's compressor, to cool specific areas of the turbine disc. The cooling effect helps to even out temperature gradients that can cause thermal stress, ultimately preventing uneven expansion and contraction which could lead to cracking or other forms of mechanical failure.

When bleed air is directed to the turbine disc, it helps maintain a more uniform temperature across the surface, which is essential as turbine discs operate in extremely high temperatures. This practice is especially critical during engine operation to mitigate the risks associated with thermal loads that are inherent in turbine operation.

The other methods mentioned do not specifically address the thermal stress relief mechanisms required for turbine discs. Adjusting rotor speed can influence operating stresses but does not specifically relieve thermal stress. Applying lubrication is crucial for reducing friction in bearings and other components but does not address thermal stress in the disc itself. Vibration management is essential for maintaining overall engine health, yet it primarily deals with dynamic loads rather than thermal stresses that require active cooling measures.