An important consideration at the design stage of a gas
turbine engine is the need to ensure that certain parts of the
engine, and in some instances certain accessories, do not
absorb heat to the extent that is detrimental to their safe
operation. The principal areas that require air cooling are
the combustor and turbine.
Cooling air is used to control the temperature of the
compressor shafts and discs by either cooling or heating
them. This ensures an even temperature distribution and
therefore improves engine efficiency by controlling thermal
growth and thus maintaining minimum blade tip and seal
clearances. Typical cooling and sealing airflows are shown
in Figure 5e1.