Handbook of Turbomachinery Second Edition Revised - Ventech!

Figure 26 Velocity triangle of steam through a steam turbine stage.
steam expanded from the pressure upstream of a stage to the downstream
pressure without losses.
The velocity of the rotating blades or wheel velocity, is designated W,
and the vector result of V1 and W is the velocity of the entering steam
relative to the rotating blade, V2. a is the angle at which the steam leaves the
stationary blade relative to the plane of rotation of the rotating blade. a is
sometimes referred to as the ‘‘nozzle angle’’ although it is actually the steam
angle and typically about 28 larger than the nozzle passage angle.
In an impulse design, there is little pressure drop across the rotating
blades so that the relative velocity leaving the rotating blade, V3 (Fig. 26),
would be equal to the entering velocity V2 if there were no frictional losses.
The absolute velocity of the exiting steam is V4, the vector sum of V3 and the
wheel speed, W. A goal of the stage design process is to have the direction of
the flow at exit be as close as possible to axial for entry into the next stage
[9].
The force on the blade is proportional to the change in tangential
components of the velocity, i.e., the entering tangential velocity, Va, less the
exit tangential velocity, Vb.
Copyright © 2003 Marcel Dekker, Inc.