Miljøudvalget 2013-14
MIU Alm.del Bilag 406
Offentligt
1382571_0001.png
Simplified upwind propagation model for
wind turbines
Model description by Birger Plovsing and Jørgen Jakobsen (based on manuscript to be
submitted to Noise Control Engineering Journal)
Input parameters
h
S
: source height (m)
d:
horizontal propagation distance (m)
u
10
: wind speed component 10 m above ground in the direction of propagation (m/s), negative
values in upwind
Fixed model parameters (cannot be changed)
h
R
= 1.5 m: receiver height
z
0
= 0.05 m: roughness length
t
0
= 10° C: air temperature
c(t
0
)
= 337,4 m/s: the sound speed at temperature
t
0
Calculation of model parameter d’
Wind speed
u
(m/s) as a function of height
z
(m):
z
10
u
(
z
)
=
u
10
ln
ln
z
0
z
0
Average sound speed gradient
Δc/Δz
(s
-1
):
∆
c u
(
h
S
)
−
u
(
h
R
)
=
∆
z
h
S
−
h
R
Effective sound speed
c
0
(m/s) at the ground (z = 0) in linear sound speed profile approximation:
∆
c
c
0
≅
c
(
t
0
)
+
u
10
−
10
∆
z
1
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1382571_0002.png
Relative sound speed gradient
a
(m
-1
):
∆
c
a
=
c
0
∆
z
Distance to shadow zone d
SZ
(m):
d
SZ
≅
2
h
S
2
h
R
+
a
a
Horizontal propagation distance relative to shadow zone distance
d’
(dimensionless):
d
d
′ =
d
SZ
Method for determining the A-weighted upwind ground effect
ΔL
u
in excess
of the A-weighted downwind ground effect
ΔL
g
given in
“Vindmøllebekendtgørelsen”:
The excess A-weighted upwind ground effect
ΔL
u
in dB is calculated by:
15
if h
S
≤
15
′
h
S
=
h
S
if
15
<
h
S
<
70
70
if h
S
≥
70
k
1
=
+
0.55
220
(
h
′ −
15
)
k
2
=
S
+
2.1
50
0
if d
′ ≤
k
1
d
′ −
k
1
if k
1
<
d
′ <
k
2
∆
L
u
= −
15
k
2
−
k
1
−
15
if d
′ ≥
k
2
(
h
S
′ −
15
)
Method for determining the upwind low frequency ground effect
ΔL
uLF
in
excess of the one-third octave band downwind ground effect
ΔL
gLF
given in
“Vindmøllebekendtgørelsen”:
For one-third octave band frequencies below 31.5 Hz
ΔL
uLF
is equal to 0 dB.
2
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1382571_0003.png
In the frequency range 31.5 Hz to 160 Hz
ΔL
uLF
in dB is calculated by the following equation where
ΔL
max
,
k
1
and
k
2
are defined in the table below:
0
if d
′ ≤
k
1
d
′ −
k
1
= ∆
L
max
if k
1
<
d
′ <
k
2
k
2
−
k
1
∆
L
max
if d
′ ≥
k
2
ΔL
max
-3
-6
-10
-14
-15
-15
-15
-15
k
1
3
2.3
2
1.7
1.6
1.5
1.45
1.35
k
2
5
5
5.2
5
4.3
3.6
3.2
3.05
∆
L
uLF
Frequency (Hz)
31.5
40
50
63
80
100
125
160
3