Taper-Twisting of blades
Reasons for taper-twisting of the final stages of LP turbines
- Due to the change in centrifugal velocity with the increase diameter
towards the exhaust end the true vector velocity of the steam varies
over the length of the nozzle. The blade must be twisted to ensure the
steam enters at the correct angle
- The tip has an aerofoil section to increase the reaction to
equalise the flow of steam across it which would otherwise be
non-uniform due to the pressure difference between the tip and base due
to centrifugal action
- The tapered blade design allows an increased distance between
the blade and nozzles. This gives water droplets more time to increase
in speed driven by the steam flow.
In addition the tangential velocity is much greater than that of the
axial velocity and hence the rotating disc of steam tends to centrifuge
out the water droplets
- When viewed as a cantilever beam the tapered design is ideal from a mechanical point of view to resist bending
- The tip aerofoil section increases the reaction to equalise the
flow of steam across the bladewhich would otherwise be non-uniform due
to the pressure difference between tip and base caused by the
centrifuged steam

No comments:
Post a Comment