Fluid Mechanics and Thermodynamics of Turbomachinery, 5e

122 Fluid Mechanics, Thermodynamics of Turbomachinery
Efficiency, %
FIG. 4.19. Cooled HP turbine rotor blade showing the cooling passages (courtesy of
Rolls-Royce plc).
90
80
70
Conway, Spey
Uncooled
ADOUR
High hub–tip ratio
Internal convection
cooling
RB 211
Internal convection
and film cooling
1300 1500 1700
1900
Turbine entry temp., K
Low hub–tip ratio
Engine test
facility results
Transpiration
cooling
FIG. 4.20. Turbine thermal efficiency vs inlet gas temperature. WILDE (1977).
and turbine of a jet engine. When a turbine can be expected to operate close to its design
incidence (i.e. in the low loss region) the turbine characteristics can be reduced to a
single curve. Figure 4.21, due to Mallinson and Lewis (1948), shows a comparison of
typical characteristics for one, two and three stages plotted as turbine overall pressure
ratio p 0II/p 0I against a mass flow coefficient m . (÷T 01)/p 0I. There is a noticeable tendency
for the characteristic to become more ellipsoidal as the number of stages is increased.
At a given pressure ratio the mass flow coefficient, or “swallowing capacity”, tends to