ESSOM COMPANY LIMITED
Section 2: Theory
10
▪
Kaplan and Axial Flow Propeller Turbines
In Kaplan propeller turbine as shown in
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, water passes through guide vanes
same as in the Francis turbine and is directed into axial direction before reaching the runner
.
The construction of the
runner is similar to a propeller
.
Propeller blade angle is often adjustable to improve efficiency characteristics
.
For the
Kaplan turbine, the guide vanes direct water radically toward the axis before turning axially toward the runner
.
The flow
is then two dimensional in planes normal to the axis of rotation where a particle of fluid remains at a constant distance
from the axis
.
The streamlines are helices on co
-
axial cylinders
.
A streamline can be shown only on a developed cylinder
for the corresponding radius
.
Figure 2- 13
:
Kaplan turbine
.
For the axial flow turbine
(
as shown in
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and
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found.
)
, the water flow toward the runner is axial
.
The guide vanes redirect the flow such that a particle of fluid remains
at a constant distance from the axis and the streamlines are helices on co
-
axial cylinder similar to Kaplan turbine
.
In both Kaplan and axial flow turbines, the guide vanes may be fixed or adjustable to redirect the streamlines
relative angle almost perpendicular to the runner blades
.
If the water head is not much variable and the load requirement
is rather stable, the fixed blade runner is most economical as high efficiency can be obtained with less mechanical part
and adjusting devices
.
