Axial-flow turbines are used in most applications involving compressible fluids. 1 They power most gas turbines except the smaller ones. Their efficiency is higher than radialinflow turbines in most operating ranges. Axial-flow turbines are also used in steam turbine applications. However, there are significant differences between the design of axial-flow turbines used in gas turbines and those used in steam turbine applications.
There are impulse and reaction-type steam turbines. Most reaction-type steam turbines have a 50 percent reaction level. This design has proven to be very efficient. The reaction level varies considerably in the blades of gas turbines. Axial-flow turbines used today have a high work factor (ratio of stage work to square of blade speed). This is done to achieve lower fuel consumption and to reduce noise from the turbine.
The important state points used to analyze the flow within a turbine are indicated at the following locations in Fig. 13.1:
0 The nozzle entrance
1 The rotor entrance
2 The rotor exit
The fluid velocity is an important parameter for analyzing the flow and energy transfer within a turbine. The fluid velocity relative to a stationary point is called the absolute velocity, V. This is an important term for analyzing the flow across a stationary blade such as a nozzle. [*] In turbine applications, the stationary blades of the turbine are called nozzles.
The relative velocity, W, is used when analyzing the flow across a rotating...
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