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