Friday, January 20, 2012

Bearing chamber cooling, Development of high pressure turbine blade cooling,High pressure nozzle guide vane construction and cooling ,Accessory cooling

Fig. 9-3 Development of high pressure turbine blade cooling.

Bearing chamber cooling

9. Air cooling of the engine bearing chambers is not normally necessary since the lubrication system
(Part 8) is adequate for cooling purposes.
Additionally, bearing chambers are located, where
possible, in the cooler regions of the engine. In instances where additional cooling is required, it is
good practice to have a double skinned bearing housing with cooling air fed into the intermediate space.
Fig. 9-4 High pressure nozzle guide vane construction and cooling
Accessory cooling

10. A considerable amount of heat is produced by some of the engine accessories, of which the
electrical generator is an example, and these may often require their own cooling circuit. When air is
used for cooling, the source may be the compressor or atmospheric air ducted from intake louvres in the
engine cowlings.

11. When an accessory unit is cooled during flight by atmospheric air it is usually necessary to provide
an induced circuit for use during static ground running when there would be no external airflow. This
is achieved by allowing compressor delivery air to pass through nozzles situated in the cooling air outlet
duct of the accessory. The air velocity through the nozzles create a low pressure area which forms an
ejector, so inducing a flow of atmospheric air through the intake louvres. To ensure that the ejector system
only operates during ground running, the flow of air from the compressor is controlled by a valve. A
generator cooling system with an ejector is shown in fig. 9-6.

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