2011 International Conference on Alternative Energy in Developing Countries and Emerging Economies
- 314 -
V. E
XTRAPOLATION
U
NCERTAINTIES
Four met masts are located on the site at the following
distances from each other:
TABLE 2
D
ISTANCE BETWEEN MET MASTS
DISTANCE
(m)
Perampuk
ettimedu
Meenaksh
ipuram
Sakkulat
humedu
Kailasam
edu
Perampukettim
edu
X
7 500
3 500
6 600
Meenakshipura
m
6 000
X
6 200
11 800
Sakkulathume
du
3 500
6200
X
5 800
Kailasamedu
6 700
11 800
5 800
X
The altitude gradients between the met masts are given
by the following table:
T
ABLE
3
A
LTITUDE GRADIENT BETWEEN MET MASTS
ALTITUDE
GRADIENT (m)
Perampuk
ettimedu
Meenaksh
ipuram
Sakkulath
umedu
Kailasame
du
Perampukettime
du
X
695
16
15
Meenakshipuram
695
X
711
680
Sakkulathumedu
16
711
X
31
Kailasamedu
15
680
31
X
The accuracy of the horizontal and vertical
extrapolation using the CFD computations is checked by
comparing the computational results to the measurements
at the met masts. To perform this validation, the
measurements at 10 m height of the mast at
Perampukettimedu and at 20 m height of the mast at
Meenakshipuram have been used as references. The mean
wind speeds have been computed at the masts
Meenakshipuram (10 m and 20 m) and Sakkulathumedu
(10 m and 20 m), Kailasamedu (10 m and 20 m)
considering the topographical coefficients computed with
meteodyn
WT
. The overall mean wind speed at
Meenakshipuram, Sakkulathumedu and Kailasamedu are
very well estimated by the software.
VI. R
ESULTS
& C
ONCLUSION
The comparison of computed and met mast results are
presented in the table 4. The mean error on the mean
wind speed estimations is about 8.34%.
TABLE 4
M
EASUREMENT DATA AT TARGET MASTS
V
S
C
OMPUTED RESULTS AT
TARGET MASTS
Name of the
stations & height
of the met mast
Measurement
data at the
target masts
(A) m/s
Computed
results at
the target
masts (B)
m/s
Difference
(A-B) m/s
Error (%)
= (A-
B)/A
Sakkulathumedu
Mean
Wind Speed at
10m (m/s)
8.33
7.76
0.57
6.8*
Kailasamedu
Mean
Wind Speed at
10m (m/s)
5.60
5.14
0.46
8.2**
Meenakshipuram
Mean
Wind Speed at
10m (m/s)
4.53
4.99
-0.46
10.2**
Sakkulathumedu
Mean
Wind Speed at
20m (m/s)
8.21
7.78
0.43
5.2*
Kailasamedu
Mean
Wind Speed at
20m (m/s)
6.25
5.95
0.3
4.8**
Meenakshipuram
Mean Wind
Speed at 20m
(m/s)
5.12
5.88
-0.76
14.8**
*computed results at the target masts based on Meenakshipuram met
mast at 20 m height
**computed results at the target masts based on Perampukettimedu
met mast at 10 m height
Both the vertical and the horizontal extrapolation have
been validated: the horizontal distance between the mast
at Sakkulathumedu and the mast at Meenakshipuram is
6200 m
and the altitude gradient between these two masts
is
711 meters
and yet the maximal error between the
measurements and the Meteodyn WT computation results
is only
6.8%.
However, as some computed points are still
not matching the results, further roughness and thermal
stability calibration has to be carried out and this study
will be implemented as the second part of this research
work. Since the actual values presented in the table 4 are
10 years old second wind measurement frequency
distribution data, the recent measurements with 10
minutes data at new sites will be verified in the future.
R
EFERENCES
[1]
P. J. Hurley (1997); An evaluation of several turbulence
schemes for the prediction of mean and turbulent fields in
complex terrain
[2]
[3]
A.N. Ross, S.B. Vosper; Neutral Turbulent flow over
forested hills
