Brochure

C
1
C
1
- C
1U
+ C
1U
U
1
C
1
W
1
W
1
W
1
No inlet rotation
Counter rotation
Co-rotation
C
1m
W
1
U
1
C
1
C
1
C
1
C
1U
C
1U
W
1
W
1
b
1
a
1
a
1
a
1
b
1
b
1
72
72
4.6 Inlet rotation
Inlet rotation means that the fluid is rotating before it enters the impeller.
The fluid can rotate in two ways: either the same way as the impeller
(co-rotation) or against the impeller (counter-rotation). Inlet rotation occurs
as a consequence of a number of dierent factors, and a dierentation
between desired and undesired inlet rotation is made. In some cases inlet
rotation can be used for correction of head and power consumption.
In multi-stage pumps the fluid still rotates when it flows out of the
guide vanes in the previous stage. The impeller itself can create an inlet
rotation because the fluid transfers the impeller’s rotation back into the inlet
through viscous eects. In practise, you can try to avoid that the impeller
itself creates inlet rotation by placing blades in the inlet. Figure 4.14 shows
how inlet rotation aects the velocity triangle in the pump inlet.
According to Euler’s pump equation, inlet rotation corresponds to C
1U
being
dierent from zero, see figure 4.14. A change of C
1U
and then also a change
in inlet rotation results in a change in head and hydraulic power. Co-rotation
results in smaller head and counter-rotation results in a larger head. It is
important to notice that this is not a loss mechanism.
Figure 4.14: Inlet velocity triangle at constant
flow and dierent inlet rotation situations.
4. Pump theory