ABSTRACT
Besides the radial-flow gas turbine, which is discussed in Chapter 7, two additional types of gas turbines are commonly used, viz., the axial-flow impulse turbine and the axial-flow reaction turbine. The axial-flow impulse turbine is discussed in Chapter 2 and in Chapter 9. As shown in Figure 2.5, the impulse turbine has a symmetrical blade profile; moreover, the velocity diagram shown in Figure 9.2 is drawn with W 2 = W 3, i.e., there is no change in the magnitude of the relative velocity of the gas in the impulse rotor. The reaction equation (2.23), when applied to the impulse rotor with inlet at station 2 and exit at station 3, shows that R = 0, i.e., the impulse turbine is a zero reaction turbomachine. Equation (9.18) shows further that h2 = h3, which, for a perfect gas, means that T 2 = T 3 and p2 = p3. In the stator or nozzle section, which is located upstream of the rotor, the gas expands and its velocity increases. Application of equations (2.9) and (2.10) to the impulse rotor yields
and
(8.1)
The latter equation is the same as (2.19) applied to an impulse rotor having stations numbered 2 and 3 at the inlet and exit, respectively.
