Environmental Engineering Reference
In-Depth Information
Table 2-7. Typical Clayton VPA Wind Segment Data
[George and Connell, 1984]
Data Segment Number
=
C2c
Date; Starting Time
=
06/30/82; 1740
VPA Hub Height,
H
C
=
30.5 m
VPA Sampling Radius,
R
C
=
19.0 m
Test Segment Length
=
8.5 min
Rotational Sampling Speed,
P
=
0.67 Hz
Center Mean Wind Speed,
U
0
=
10.71 m/s
=
0.856 m/s
Center Stationary Turbulence, s
0
=
1.506 m/s
Wind Shear Across Disk, D
U
Frequency band
f
(Hz)
Mid-band harmonic
frequency
f/P
Variance
μ
(m/s
2
)
Turbulence
s
(m/s)
Turbulence intensity
s/
U
0
< 0.33
0.498
0.706
0.066
0.33 - 1.00
1
0.431
0.656
0.061
1.00 - 1.67
2
0.146
0.382
0.036
1.67 - 2.33
3
0.070
0.264
0.025
2.33 - 3.00
4
0.037
0.192
0.018
3.00 - 3.67
5
0.032
0.179
0.017
-
Turbulence intensities of harmonics above the irst decrease with increasing
harmonic number, following a roughly exponential decay.
-
Atmospheric stability has little, if any, direct effect on harmonic turbulence in-
tensities. An indirect effect of a stable atmosphere on the irst harmonic inten-
sity is through the increased wind shear often present in a stable atmosphere.
These observations lead to the following model for representing the Clayton VPA data:
(s
1
/
U
0
)
C
= 0.0311 + 0.297 D
U
/
U
0
(2-28a)
(s
n
/
U
0
)
C
= 0.059
n
-
0.75
n
> 1
(2-28b)
where
s
n
= rotationally-sampled turbulence in the frequency range from (
n
- ½)
P
to
(
n
+ ½)
P
(m/s)
P
= rotational sampling frequency (rad/s)
C
= subscript denoting Clayton VPA parameters
H
= hub elevation above ground level (m)
R
= radius of circular sampling path (m)
U
0
= steady free-stream wind speed at hub elevation (m/s)
D
U
= total steady wind shear from top to bottom of circular sampling path (m/s)
We can determine the steady wind shear across the circular path, D
U
, from anemometer
test data, or we can estimate it using one of several models, including the well-known
power
Search WWH ::
Custom Search