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