Environmental Engineering Reference
In-Depth Information
Table 1: Category I models [ 4 ].
No.
Model
1
L
=
10 log
P
+
50
WA
10
WT
L
=
22 log
D
+
72
2
WA
10
⎛
A
⎞
D
b
LC
=
log
VC
+
log
n
+
C
log
CC
+
log
−
C
log
DC
−
3
⎜
⎟
pA
1
10
tip
2
10
b
3
10
T
4
10
5
10
6
⎝
A
⎠
r
r
during the years. Lowson (cited in [4]) divided the prediction models in three
categories:
•
The Category I models predict the global emitted noise as a function of main
wind turbine parameters, like rated power, rotor diameter, blade area, tip
speed, etc.
The Category II models are semi-empirical relationships which predict the total
•
sound pressure level and spectral shape taking into account the various noise
generation mechanisms.
The Category III models are based on a detailed description of the rotor geometry
•
and aerodynamics and give detailed information about the acoustic fi eld.
6.1 Category I models
These models are the simplest ones. Based on simple algebraic relations they
predict the emitted sound power level as functions of the wind turbine main
parameters. Table 1 lists the category I models as it is summarized by Wagner
et al.
[ 4 ]. In Table 1
L
WA
is the total A-weighted sound power level,
P
WT
the rated
power of the turbine,
D
the rotor diameter,
L
pA
the A-weighted sound pressure
level at a monitoring point located at a distance of
r
0
from the tower base,
V
tip
the
tip speed,
n
b
the number of the blades,
A
b
the blade area,
A
r
the rotor area,
C
T
the
axial force coeffi cient,
r
the hub
observer distance.
C
i
are empirical parameters
having different values in different references.
These Category I models are simple and fast, however they are by far not univer-
sal. As a consequence, these models were rapidly outranked by the computationally
not much more expensive, but more accurate Category II models.
−
6.2 Category II models
The models belonging to this category are semi-empirical and consist of a set
of models for the noise generation mechanisms listed in Section 4.1.2. Based on
Lighthill's and Ffowcs Williams
−
Hawkings theory and experimental measurements
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