Environmental Engineering Reference
In-Depth Information
Fig. 7.8
The philosophy of
k
opt
2
ω
t
b
=
n
r
According to these two times, three operation scenarios can be recognised [
11
],
these are:
1. t
b
[ t
w
: This scenario corresponds to slow rotation in which some undisturbed
wind passes the area swept by the rotor without harvesting its power content.
2. t
b
\ t
w
: This scenario corresponds to fast rotation in which the blade passes
through the disturbed wind component generated by the previous blade. In this
case, the rotor acts as a rigid obstacle and prevents the undisturbed wind from
passing through the rotor.
3. t
b
t
w
: This scenario corresponds to the optimal operation in which the blade
harvests the power from the re-established wind component.
Suppose the length of the disturbed wind is S(m) and n is the number of blades,
then t
b
and t
w
are obtained as follows:
9
=
t
b
¼
2p
x
r
n
t
w
¼
S
v
ð
7
:
18
Þ
;
by setting t
b
equal to t
w
, the optimal rotational speed thus given as:
x
ropt
¼
2pv
nS
ð
7
:
19
Þ
