244
6 Steam Turbines
q 1 ~ 2 × 80°, h 4 = 25 mm, q 4 = 360°; 50 % reaction: 7 stages, h 1 ~ 15 mm (ideal
minimum height cannot be obtained).
b. Design the nozzles and the rotor blades. Take the Curtis stage as an example.
A: Curtis: Z s = 32, b throat = 12 mm, b 1 = 15.5 mm. Z r = 150, c a   ≈  35  mm, 
b 1 = 7.45 mm. The rotor blades may be drawn as in Fig. 6.34, except that the
leading edge should stay sharp as the inlet Mach number is above unity. The stator vanes may be drawn as in Fig 6.37, but the nozzle channels are convergentdivergent here: see Fig 6.39. The positions of the points B, C and E should be
chosen such that the resulting profile is smooth.
6.10.7. Figure 6.40 is a sketch of a Girard turbine. It is an axial hydraulic turbine
of impulse type developed around 1850. The rotor turns in the atmosphere. Therefore, pressure at the rotor inlet and outlet is atmospheric pressure. The zero presFig. 6.39 Stator vane profile; supercritical flow; initial shape
Fig. 6.38 Velocity triangles for the last stage of
the LP part