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Axial-flow Turbines: Two-dimensional Theory 127
Y
D
U
C 2
W 2
L X
L X
a
Y D
a
a
W 1
U
a
C 1
W 1
(a)
W 1
C 1
U
W 1
-a D
a
Y
a
L X
L
X
W 2
C 2
D
U Y
(b)
FIG. 4.25. Velocity and force vectors acting on a blade of a Wells turbine in motion:
(a) upward absolute flow onto blade moving at speed U ; (b) downward absolute flow
onto blade moving at speed U .
Two-dimensional flow analysis
The performance of the Wells turbine can be predicted by means of blade element
theory. In this analysis the turbine annulus is considered to be made up of a series of
concentric elementary rings, each ring being treated separately as a two-dimensional
cascade.
