Wind energy II. Lesson 2. Wind speed measurement
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Transcript of Wind energy II. Lesson 2. Wind speed measurement
Wind Energy I
Michael Hölling, WS 2010/2011 slide 1
Wind speed measurements
Wind Energy I
slideMichael Hölling, WS 2010/2011 2
Class content
4 Wind power
5 Wind turbines in general 6 Wind - blades
interaction
7 Π-theorem
8 Wind turbine characterization
9 Control strategies
10 Generator
11 Electrics / grid
3 Wind field characterization
2 Wind measurements
Wind Energy I
slideMichael Hölling, WS 2010/2011 3
Wind speed measurements
1. Pressure sensors - e.g. Prandtl tube with manometer
2. Cup anemometer
3. Ultrasonic anemometer (USA)
4. Light detection and ranging (LiDAR)
5. New developments - e.g. sphere anemometer
Wind Energy I
slideMichael Hölling, WS 2010/2011 4
Sensor resolution
Temporal and spatial resolution
Taylor’s hypothesis - picture of frozen turbulence:
temporal resolution limits spatial resolution AND spatial resolution limits temporal resolution
!u
!u" << 1
“Eddies have much longer life-time than they need to travel past a sensor”
Wind Energy I
slideMichael Hölling, WS 2010/2011 5
Pressure measurements
Why should we measure the pressure ?
Prandtl tube
Bernoulli equation: ptotal = pdyn + pstatic
with: pdyn = 1/2 · !air · u2
Wind Energy I
slideMichael Hölling, WS 2010/2011 6
Pressure measurements
Measure the pressure e.g. with an “inclined tube manometer”
Therefore the velocity is given by:
u =
!2 · (ptotal ! pstatic)
!air
Wind Energy I
slideMichael Hölling, WS 2010/2011 7
Cup anemometry
u urot
Why this basic design ?
Wind Energy I
slideMichael Hölling, WS 2010/2011 8
Cup anemometry
Different models
Wind Energy I
slideMichael Hölling, WS 2010/2011 9
Cup anemometry
Calibration
optoelectronic detection
inductive detection
0 1000 2000 3000 4000 5000
01
23
45
t[s]
U[V]
t [s]
U [
V]
f [Hz]
u [m
/s]
Wind Energy I
slideMichael Hölling, WS 2010/2011 10
Cup anemometry
Over-speeding
measured turbulence intensity measured turbulence intensity
33% 8%
t [s]v
[m/s
]
gusts at 2/3 Hz, 9 m/s
hot-wire anemometer cup anemometer
u [m
/s]
Wind Energy I
slideMichael Hölling, WS 2010/2011 11
Inclined flow
Cup anemometry
-0,2
-0,18
-0,16
-0,14
-0,12
-0,1
-0,08
-0,06
-0,04
-0,02
0
0,02
0,04
0,06
0,08
0,1
-34 -32 -30 -28 -26 -24 -22 -20 -18 -16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34
rel.
de
via
tio
n o
f a
ne
mo
em
ter
fre
qu
en
cy
tilt angle /°
tilt response anemometer Type 3.3351.00.000 , serial 0807011 at ca. 10 m/s
dataset 1796_09
dev. V anemo at 1Hz dev. V anemo bin average
nozzle
+20°
nozzle
-20°
Wind Energy I
slideMichael Hölling, WS 2010/2011 12
Cup anemometry
Summary
low temporal resolution (about 1Hz)
effected by inertia
not sensitive to wind direction
moving parts result in
wear of bearings
sensitive to icing
www.thiesclima.com
Wind Energy I
slideMichael Hölling, WS 2010/2011 13
Ultrasonic anemometry
Measurement principle
Wind Energy I
slideMichael Hölling, WS 2010/2011 14
Different models - 2D and 3D
Ultrasonic anemometry
Wind Energy I
slideMichael Hölling, WS 2010/2011 15
Ultrasonic anemometry
u
Drawbacks
supports create wakes
system is expensive
Deviation from horizontal velocity
Wind Energy I
slideMichael Hölling, WS 2010/2011 16
LiDAR
Measurement principle
Wind Energy I
slideMichael Hölling, WS 2010/2011 17
Possibilities with LiDAR
LiDAR
Wind Energy I
slideMichael Hölling, WS 2010/2011 18
Sphere anemometer
Motivation alternative to
cup anemometry --> 1D, 1Hz, wear of bearings, over-speeding
ultrasonic anemometry --> expensive, wake effects of transducer supports
Properties wind velocity and direction measurements
temporal resolution up to resonance frequency
Wind Energy I
slideMichael Hölling, WS 2010/2011 19
Sphere anemometer
Measurement principle
deflection of a flexible tube due to drag forces acting
with general expression for drag force
drag coefficient considered constant for leads to
F =12
· ! · A · cD · v2
cD
s ! v2 " v = m ·#
s
Easy calibration function!
Re ! 103 . . . 2 · 105
s =l3
E · J·!
Fs
3+
Ft
8
"
Wind Energy I
slideMichael Hölling, WS 2010/2011 19
Sphere anemometer
Measurement principle
deflection of a flexible tube due to drag forces acting
with general expression for drag force
drag coefficient considered constant for leads to
F =12
· ! · A · cD · v2
cD
s ! v2 " v = m ·#
s
Easy calibration function!
Re ! 103 . . . 2 · 105
Rohr
Laser
Kugel
2D-PSD
Gewinde
l
sphere
laser
tube
s =l3
E · J·!
Fs
3+
Ft
8
"
Wind Energy I
slideMichael Hölling, WS 2010/2011 20
Sphere anemometer
–0.3 –0.2 –0.1 0.0 0.1 0.2 0.3
–0.3
–0.2
–0.1
0.0
0.1
0.2
0.3
Uy [V]
Ux [
V]
0
1
2
3
5
7
9
11
14
17
20
v [m/s]
0°
270°
90°
180°
!
Calibration
Wind Energy I
slideMichael Hölling, WS 2010/2011 21
Sphere anemometer
Gusts measurements
Wind Energy I
slideMichael Hölling, WS 2010/2011 22
Sphere anemometer
Comparison of time series
measured turbulence intensities measured turbulence intensities measured turbulence intensities 33% 32% 8%
hot-wire anemometer sphere cup anemometer
t [s]
u [m
/s]
Wind Energy I
slideMichael Hölling, WS 2010/2011 23
Comparison of power spectra
Sphere anemometer
Wind Energy I
slideMichael Hölling, WS 2010/2011 24
Sphere anemometer
2007 2008 2009 2010
“Evolution” of sphere anemometer