Page 61 - The Jet Engine

11. The losses which prevent the turbine from being
100 per cent efficient are due to a number of
reasons. A typical uncooled three-stage turbine
would suffer a 3.5 per cent loss because of
aerodynamic losses in the turbine blades. A further
4.5 per cent loss would be incurred by aerodynamic
losses in the nozzle guide vanes, gas leakage over
the turbine blade tips and exhaust system losses;
these losses are of approximately equal proportions.
The total losses result in an overall efficiency of
approximately 92 per cent.
CONSTRUCTION

12. The basic components of the turbine are the
combustion discharge nozzles, the nozzle guide
vanes, the turbine discs and the turbine blades. The
rotating assembly is carried on bearings mounted in
the turbine casing and the turbine shaft may be
common to the compressor shaft or connected to it
by a self-aligning coupling.
Nozzle guide vanes
13. The nozzle guide vanes are of an aerofoil shape
with the passage between adjacent vanes forming a
convergent duct. The vanes are located (fig. 5-8) in
Fig. 5-6 A typical turbine blade showing the turbine casing in a manner that allows for
twisted contour. expansion.

Fig. 5-7 Gas flow pattern through nozzle and blade.

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