Environmental Engineering Reference
In-Depth Information
KKK Re 10 M
Clean Re 10,3 M
Zig-Zag Tape Re 10,2 M
Zig-Zag Tape Re 10,3 M
Carobrundum Re 10,2 M
KKK Re 10 M
1.6
1.6
1.4
1.4
Clean Re 10,3 M
Z
ig-Zag Tape Re 10,2 M
Zig-Zag Tape Re 10,3 M
C
arobrundum Re 10,2 M
1.2
1.2
1
1
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0
0
-4
-2
0
2
4
6
8
10
12
0
0.005
0.01
0.015
0.02
0.025
Angle of attack (deg)
Drag coefficient
Figure 23: Polars of DU-W-300 mod at Reynolds number 10 million.
KKK Zig-Zag-Tape rougness, RE varying
Zig-Zag x/l = 0.3 Re 2,2 M
Zig-Zag x/l = 0.3 Re 7.8 M
Zig-Zag x/l = 0.3 Re 8,9 M
Zig-Zag x/l = 0.3 Re 10,4 M
Zig-zag x/l = 0.2 Re 2,3 M
Clean Re 2,2 M
KKK Zig-Zag-Tape roughenss, RE varying
Zig-Zag x/l = 0.3 Re 2,2 M
Zig-Zag x/l = 0.3 Re 7.8 M
Zig-Zag x/l = 0.3 Re 8,9 M
Zig-Zag x/l = 0.3 Re 10,4 M
Zig-zag x/l = 0.2 Re 2,3 M
Clean Re 2,2 M
1.6
1.6
1.4
1.4
1.2
1.2
1
1
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0
0
-4
-2
0
2
4
6
8
10
12
14
0
0.005
0.01
0.015
0.02
0.025
Angle of attack (deg)
Angel of attack (deg)
Figure 24: Polars of DU-W-300 mod with zig-zag tape, Reynolds number varying.
turbine with a vertical axis of rotation (VAWT) and the second are diffuser aug-
mented wind turbines. A discussion of
counter-rotating
systems is ommitted here.
The reader may fi nd information in [ 48 , 32 ].
Two types of VAWT are possible (see Fig. 25): those driven by drag (Savonius)
and those driven by lift (Darrieus). Aerodynamic modeling starts with the question
whether an actuator
disk
modeling makes any sense. The total structure is an
extended one, so at least two disks for up-wind and down-wind halves have to be
used. This
double actuator disk
model was formulated by Loth and Mc Coy [70].
Only circumferential averaged values are discussed. The usual momentum theory
for two
independent
disk was applied. As a result of these assumptions only one
optimization parameter
a
- the (global) velocity interference factor - remains, giv-
ing
. Further, the power extraction is seen to split into 80 and 20 %
shares for the fi rst and second disk respectively.
Figure 26 shows the fi ndings in a graph. It is stricking that the total (normal-
ized) power is >0.6 along the range 0.1 <
a <
0.42. Here
a
was defi ned as usual
as
a
:=
v
disk
/
v
∝
. It should be noted that such high
c
P
s have not been observed
so far. As an important design parameter the
solidity
s
=
Bc/R
(
B
= number of
blades;
c
= chord and
R
= rotor radius) is used. It can easily be shown that low
s
corresponds to high TSR but unfortunately then there is
no
self-starting [ 67 ]
behavior. Only when using high
s
max,
dAD
c
= 0.64
P
≥
0.4 can a self-staring turbine be
achieved.
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