DTU Wind Speed Course Cups

7/28/2019 DTU Wind Speed Course Cups

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46400 Wind Speed Measurements - Cups

T F Pedersen Oct 20121 DTU Wind Energy Department

Troels Friis Pedersen

Professor, Ris DTU Wind Energy Division

Wind Speed Measurements in Wind Energy

Average wind speed measurements

- Cup anemometry

Turbulence measurements

-Sonic anemometry

-Cup anemometry


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Cup anemometry used for:- wind resource assessment (low power consumption, low

cost)

- power performance measurements (accuracy, traceability)

- wind turbine control (robust, maintainable)

Sonic anemometry used for:

- site turbulence measurements (3D wind, fast response)

- wind turbine control (2D, robust, maintainable)


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Example of types commonly used in wind energy

NRG WindSensor (Ris) Vector ThiesMaximum 40 P2546a A100L2 First Class

Cup anemometry


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Components of acup anemometer

1. Cup anemometer body

(rotational symmetric)2. Cup (three)3. Shaft4. Dust labyrinth5. Bearings6. Pulse generator7. Pulse detection

8. Cable connection (centered)9. Mounting (on tube)10. Top pin (optional for

cosine tilt response)

Cup anemometry


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Wind Speed Measurement Uncertainty- the driving parameter in windmeasurements in wind energy:

In wind energy an uncertainty of lessthan 1% is required

(WMO, World Meteorology

Organization, only requires anaccuracy of 5% on anemometers)


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An Example - cup anemometer wind speedmeasurement uncertainty

1.Cup anemometry is required in power performance measurements2.Wind speed measurement uncertainties relates to:

Calibration Field operation Mast and boom flow distortion

Terrain effects (power performance measurements)3.Calibration standard uncertainty 0.07-0.15m/s(Round Robin calibrations within 1%)

4.Field operation uncertainties 1% to 5%5.Mast flow distortion 1% to 5% (boom mounted)6.Boom flow distortion 0.5% (boom mounted)7.Terrain effects 2% to 3% (performance measurements)

Total uncertainty (boom mounted) 2.8% to 7.8% at 10m/s!(Uncertainty in Cp 8.6% to 25.4% at 10m/s!)Total uncertainty (topmounted, excl. terrain effects and bestpractice) about 1.6%


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Cup anemometer calibration


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Cup anemometer calibration

General calibration expression:

= +cal calU A F B

Where F is pulse frequencyWe also have:

2

= +cal cal

NU A B

Where N is number of pulses

per revolution and is angular

speed in rad/s


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Influence due to field operational conditions (turbulence, temp, etc.)

(graph: SITEPARIDEN/DEWI)

Field comparison of cup anemometers

Thies Classic

(reference)

Ris

Vector

Vaisala

Thies

Compact


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Field Comparison of Thies Classic and Ris P2546 Cup Anemometers(Ris boom)

Field comparison of cup anemometers

Relative deviations Thies vs RIS per Ti

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

0.11

0.120.13

0.14

0.15

0 1 2 3 4 5 6 7 8 9 10 11 12

RIS [m/s]

(Thies-R

IS)/RIS

Ti


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Angular respose RIS P2546 Cup Anemometer

0,86

0,88

0,90

0,92

0,94

0,96

0,981,00

1,02

1,04

-45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45

Tilt angle (positive from above) [deg]

RelativeSpeed

5 m/s8 m/s

8 m/s rep11 m/sCos

Tilt response measurements(Re Dahlberg FOI)

Characteristics of cup anemometers


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Influence of turbulence on inflow angleIn the field the inflow angle is not constant.Over 10min the inflow angle typically varies with a Gaussian distribution(x=value, =average value, =std.dev. )


2

2

2

( )( )

2

,

1( )

2

x

x e

=


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Tilt responseApplying a Gaussian inclination angle distribution tomeasured til t characterist ics, Ris P2546


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Tilt responseApplying a Gaussian inclination angle distribution tomeasured tilt characterist ics, Thies classic


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Tilt responseApplying a Gaussian inclination angle distribution tomeasured til t characterist ics, Vaisala


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Tilt responseApplying a Gaussian inclination angle distribution tomeasured tilt characterist ics, Vector


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Tilt responseApplying a Gaussian inclination angle distribution tomeasured tilt characterist ics, Thies Compact


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Tilt responseApplying a Gaussian inclination angle distribution tomeasured ti lt characterist ics, ACCUWIND


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Measured rotor torque measured on onecup in wind tunnel

Measured Torque Characteristics for one RIS cup

-4

-3

-2

-1

0

1

2

3

4

5

0 2 4 6 8 10 12

Wind speed (m/s)

Torque(mNm

) Ome=25 rad/s

Ome=40 rad/sOme=55 rad/s

Poly. (Ome=25 rad/s)

Poly. (Ome=40 rad/s)

Poly. (Ome=55 rad/s) Measured Torque Characteristics for one RIS cup

-6

-4

-2

0

2

4

6

0 20 40 60 80

Angular speed (rad/s)

Torque(mNm) Wsp=5 m/sWsp=8m/s

Wsp=11m/s

Poly. (Wsp=5 m/s)

Poly. (Wsp=8m/s)

Poly. (Wsp=11m/s)


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Characteristics of cup anemometersNormalised rotor torque

Note: Parabolic fit is not sufficient!

RIS Normalised Torque Coefficient

-5.0

-4.0

-3.0

-2.0

-1.0

0.0

1.0

2.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Speed ratio

Cq

Ome=25

Ome=40

Ome=55

U=5

U=8

U=11

U=8, Tu=16, f=2

Parabola fit

2( ) 1

2

A

QA

eq

Q

CARU

=

Measured rotor torque measured on onecup in wind tunnel, normalisation of torque


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-16

-14

-12

-10

-8

-6

-4

-2

0

2

46

8

10

15 20 25 30 35 40 45 50 55 60 65 70

Angular speed rad/s

TorquemNm

Ris P2546 cup anemometer ( Re Dahlberg FOI)


Measurement of aerodynamic torquewith torque sensor and thin rod


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Normalisation of aerodynamic torque


Aerodynamic Torque Coeff ic ient o f RIS P2546

-1,8

-1,6

-1,4

-1,2

-1,0

-0,8

-0,6

-0,4

-0,2

0,0

0,20,4

0,6

0,8

1,0

0,10 0,15 0,20 0,25 0,30 0,35 0,40 0,45 0,50 0,55

Speed ratio lambda

T

orqueCoefficientCqa

0

20

40

60

80

100

120

Cqa

Cqa fitWeight function


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Aerodynamic torque coefficient ofvarious cup anemometers

Torque Coefficients

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60

Speed Ratio

Cq

ThiesClasscupRISThiesCompactIdeal



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Overspeeding measurements in tunnel with

varying wind speedFOI wind tunnel with test

section in the middle. Inlet from

the right and centrifugal blower

on the left. Wind speed is

varied cyclicly in the tunnel

Rotating outlet w ind vanes and

pitot tubes. Pitot tube

measurements compared to cup

anemometer rotor


(Dahlberg, FOI wind tunnel)


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Overspeeding measurements(Dahlberg, FOI wind tunnel)


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Overspeeding measurements(Dahlberg, FOI wind tunnel)


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Friction measurements on cup anemometersFlywheel testing in climate chamber

Flywheel

Rubber

wheel

Blower

Activation

mechanism

Motor

Characteristics of cup anemometersMeasurement of friction in bearings


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The describing differential equation of the deceleration is:

4 3 1/ 2( ) 0.616 ( )d

I F R

dt

=

where ( )F is the friction in bearings as function of angular speed, and the second term is the air friction of

the flywheel with the radius R. The friction in bearings is determined by rearranging:

4 3 1/ 2( ) 0.616 ( )d

F I Rdt

=

A third degree polynomial was fitted to the deceleration, and the derivative was taken from the fit. Thefriction was again fitted to a second order polynomial.

21 2 3( )F f f f = + +

Friction measurements on cup anemometers

Characteristics of cup anemometersMeasurement of friction in bearings


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RIS P2546 cup anemometer - Flywheel tests Reproducability

10

20

30

40

50

60

70

80

90

1 2 3 4 5 6 7 8

Time [s]

Angularspeed[rad/s]

-18deg

-18deg

-18deg

-18deg

-18deg

Characteristics of cup anemometersFriction


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RIS P2546 cup anemometer - Flywheel tests

0,0E+00

1,0E-04

2,0E-04

3,0E-04

4,0E-04

5,0E-04

6,0E-04

10 20 30 40 50 60 70 80 90

Angular Speed [rad/s]

FrictionTorque[Nm]

-18deg

-18deg

-18deg

-18deg

-18deg



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Friction measurements on cup anemometersRIS P2546 cup anemometer - Flywheel tests

0,0E+00

1,0E-04

2,0E-04

3,0E-04

4,0E-04

5,0E-04

6,0E-04

10 20 30 40 50 60 70 80 90


FrictionTorque[Nm]

40deg35deg30deg25deg20deg

15deg10deg8deg6deg4deg2deg0deg-2deg-4deg-6deg-8deg-10deg-12deg-14deg-16deg-18deg-20deg



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Friction measurements on cup anemometersRIS P2546 cup anemometer - Flywheel tests

0,0E+00

1,0E-05

2,0E-05

3,0E-05

4,0E-05

5,0E-05

6,0E-05

10 20 30 40 50 60 70 80 90


FrictionTorque[Nm]

40deg35deg30deg25deg20deg

15deg10deg8deg6deg4deg2deg0deg-2deg-4deg-6deg-8deg-10deg-12deg-14deg-16deg-18deg-20deg



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Friction of RIS P2546 as Funct ion of Temperature

0,0E+00

5,0E-05

1,0E-041,5E-04

2,0E-04

2,5E-04

3,0E-04

3,5E-04

4,0E-04

4,5E-04

5,0E-04

5,5E-04

-25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45

Temperature degC

FrictionNm 20rad/s

40rad/s60rad/s80rad/s



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Friction is reduced within the first weeks of operation.New cup anemometers must be run-in before being used inmeasurements

Characteristics of cup anemometersRunning-in of cup anemometers


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From the oscillations, the inertia can be found from the formula:

l

M g rTI

2

22

4=

where: T is average time of one oscillationM is mass of rotor

r is radius from axis of rotation to the three strings

l is the length of the stringsg is gravity acceleration 9,81m/s2

For the RIS P2546 cup anemometer, the values are:

0,062M kg=

0,075r m=

0,875l m=

Measurement of rotor inertia

Characteristics of cup anemometersRotor inertia

S C


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Modeling cup anemometers

Three models are considered:1.General time domain modelA model with a detailed description of the torque coefficient curve (a modelthat can be generally applied, and which is accurate enough for classification,being used in IEC61400-12-1)

2.Parabolic torque coefficient modelA model with a parabolic torque coefficient curve (a more simple model thatcan be applied for analysis purposes)

3.Drag coefficient modelA model with a parabolic torque coefficient curve based on a general high drag

and low drag on either side of the rotor (an even more simple model that canbe applied for more simple analysis)

46400 Wi d S d M t C


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Modeling cup anemometers1. General time domain model

The response of the cup anemometer is derived from the driving torque differential

equation, where the torque on the rotor is a sum of aerodynamic torque and friction

torque:

A f

dI Q Qdt

= +

Numerically, the response of a cup anemometer can then be calculated by small

time steps t by:

A fQ Qt

I

+ =

The output of the cup anemometer cal calU A F B= + , where / 2F N = , can be

compared to the horizontal wind speed2 2

horU u v= + , which is the wind speed

definition in the standard IEC61400-12-1



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The aerodynamic torque AQ is a function of the instantaneous wind speed vector{ }, ,U u v w=

with the inflow angle and the scalar:

2 2 2

2 2tan

wA U u v w

u v = = + +

+

The aerodynamic torque may be divided into two components, one based on the

influence of the inflow angle (tilt or angular response F), the other (the dynamic

component) on the influence of an equivalent wind speed:

( , )eqU F U U =

The aerodynamic torque can now be expressed as:

21 ( )2

A eq QAQ ARU C =

where: is the air density

A is the projected area of one cup

R is the radius to cup centre

eqU is the equivalent wind speed (in the horizontal plane)

QAC is the generalized aerodynamic rotor torque coefficient




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The generalized aerodynamic rotor torque coefficient is derived from wind tunnel

torque measurements with the cup anemometer in vertical position and whereeq

U

in this case is equal to the tunnel wind speed:

2

( )1

2

AQA

eq

QC

ARU

=

The generalized aerodynamic rotor torque coefficient is a function of the speed

ratio:

eq t

R

U U

=

where:

is angular speed of cup anemometer rotortU is a threshold wind speed

The friction torque is a function of the temperature and the rotational speed, and is

found form friction measurements:

( , )f f

Q Q T =




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Fitting of model to calibration dataDeviation of calibration points from line

-0,030

-0,020

-0,010

0,000

0,010

0,020

0,030

0,040

0,050

0 2 4 6 8 10 12 14 16 18

Wind speed [m/s]

Deviation[m/s]

cali deviation

simu deviation




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Influence of Temperature Variations from Reference Case

-0,20

-0,18

-0,16-0,14

-0,12

-0,10

-0,08

-0,06

-0,04

-0,02

0,00

-30 -20 -10 0 10 20 30 40 50

Temperature [degC]

deviation"Measured"[m/s]

Temp

Simulation of influence of external meteorological parameters

average wind speed 10m/s

turbulence intensity 10%

isotropic turbulence

length scale 500m air temperature 10C

air density 1,23kg/m3

slope of terrain 0

Reference external conditions




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Influence of Air Density Variations from Reference Case

-0,10

-0,09

-0,08

-0,07

-0,06

-0,05

-0,04

-0,03

-0,02

-0,01

0,00

0,80 0,85 0,90 0,95 1,00 1,05 1,10 1,15 1,20 1,25 1,30 1,35 1,40

Air densi ty [kg/m^3]

De

viation"Measured"[m/s

]

Dens





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Influence of Turbulence Intensity Variations from Reference Case

-0,14

-0,12

-0,10

-0,08

-0,06

-0,04

-0,02

0,00

0,02

0,00 0,05 0,10 0,15 0,20 0,25 0,30 0,35

Turbulence Intensity

Dev

iation"Measured"[m/s]

Turb



46400 Wind Speed Meas rements C ps


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Influence of Length Scale Variations from Reference Case

-0,10

-0,08

-0,06

-0,04

-0,02

0,00

0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200

Length Scale [m]

De


]

Scale



46400 Wind Speed Measurements Cups


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Influence of Slope Variations f rom Reference Case

-0,50

-0,45

-0,40-0,35

-0,30

-0,25

-0,20

-0,15

-0,10

-0,05

0,00

0,05

0,10

-30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30

Slope [deg]

De


]

Slope





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Overspeeding of RIS P2546 Cup anemometer at 23% turbulence

-1,0

-0,5

0,0

0,5

1,0

1,5

2,0

2,5

3,0

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0

Gust frequency (Hz)

Overspeeding%

measured points

simulation polynomia

simulation table

Overspeeding measurements, FOI wind tunnel, Re. TFP




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The parabolic torque coefficient model assumes the torque coefficient to be parabolic.For simplicity the friction is set to zero. The parabola has a proportionality factor

and the two roots 0 and1:

0 12

( ) ( )( )1

2

AQA

eq

QC

ARU

= =

-7

-6

-5-4

-3

-2

-1

0

1

2

3

4

-2 -1.5 -1 -0.5 0 0.5 1

Speed r atio lambda

Tor

quecoefficientCq

Modeling cup anemometers2. Parabolic torque coefficient model



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The torque coefficient curve crosses the x-axis at the equilibrium speed ratio 0 ,

which corresponds to speed ratio at calibration:

00

0

( )t t

t

R RU U U U

U U R

= = + =

The anemometer is normally calibrated in wind tunnel at equilibrium speed ratio.

The calibration expression, where N is the number of pulses per revolution, is:

2( )

2

= + = + =

cal cal cal cal cal

cal

NU A F B A B U B

N A

From these relations the calibration coefficients can be found by:

0

2cal cal t

RA B UN

= =




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Maximum overspeeding level (for high frequencies of wind

variations)

The general torque equation is:

2

0 1

1( )( )

2eq

dQ I ARU

dt

= =

Assuming the threshold wind speed to be zero, and rearranging, the governingdifferential equation is:

23 2 2

0 1 0 1

1 1 1 1( ) ( ( )) ( )2 2 2

dAR AR U AR U

dt I I I

= + +

The maximum overspeeding level (constant overspeeding at high wind speed

frequencies) with the parabolic torque coefficient model can be derived as:

)4)1(1(21 2

0

12

0

1

0

1, is T=O

+

Approximation by a second order Taylor series expansion around Ti=0 gives:

22

1

0

2

01

1

,

1

1iOiis TFTTO =

=




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2. Parabolic torque coefficient model

First order amplitude response

With time constant

And cut-off frequency

Second order critically dampedoverspeeding response withsame time constant

0.001 0.01 0.1 1 10 100

Wind speed frequency (Hz)

0.001

0.01

0.1

1

A

mplituderesponse

0.001 0.01 0.1 1 10 100

Wind speed frequency (Hz)

0.0001

0.001

0.01

0.1

1

10

Dynamicoverspee

ding(%)

21

,1 0

s iO T

0

( ) 1( )

( ( ) ) 1t

s RG s

U s U s

= =

+

1

2f

=




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Modeling of cup anemometers3. Drag coefficient model

area A

R

DH

DL

U

area A

seen from the front

seen from above

The drag coefficient model assumes constant drag coefficients on two cups on either

side of the rotor. The aerodynamic torque is then:

2 2

H L DH DLA

1Q = R( - ) = AR((U - R - (U + R )) )C CD D

2

If friction is neglected the torque equation is:

2 2(( ) ( ) )2

DH DL

d ARQ I U R C U R C

dt

= = +

Rearranging, the governing differential equation is:2 3 2

2 1( ( )) ( ( )) ( ( ))2 2

DH DL DH DL DH DL

d AR U ARC C U AR C C C C

dt I I I

= + +



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Maximum overspeeding level

The maximum overspeeding for the drag coefficient model can be derived as:

)k-(1

T)k-(1-4k-k2

=O 2i

2

s

2

,

A Taylor series expansion around Ti=0 leads to the simple relation:

2

00

22

2

,)1)(1(4

)1(iO

i

is TFT

Tk

kO =

+=

+

Assuming 0tU = we have /R U = and:

21 ((1 ) (1 ) )2

DH DLQ ARU C C = +

Setting 0Q = at torque equilibrium we find the two roots:

0 1

0

1 1 1 /1 1

DL DH k k where k C C k k

+= = = =+

Modeling of cup anemometers3. Drag coefficient model

-10

0

10

20

30

40

-1 -0,5 0 0,5 1 1,5 2 2,5 3 3,5 4Torque

coefficien

t

Cq

Speed ratio l ambda



53/70



Modeling of cup anemometers

Parabolic torque coefficient model and drag modelMaximum overspeeding level Os,max=F0*Ti

2

Overspeeding factor Fo (Os,max=Fo*Ti 2)

-0,6

-0,4

-0,2

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

1,8

2

-2 -1,5 -1 -0,5 0 0,5 1 1,5 2 2,5 3 3,5 4

lambda1 (for lambda0=0,3)

Fo

Parabolic model

Drag model

lambda0=0,3

lambda1lambda0

Drag model:

lambda1=1/lambda0



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Modeling of cup anemometers

Parabolic torque coefficient model and drag modelTorque coefficients

-4

-3

-2

-1

0

1

2

-1 -0,5 0 0,5 1 1,5 2 2,5 3 3,5 4

Lambda

Cq

Drag model

Zero overspeedingStraight lineIntermediate



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Field operation of cup anemometers - Classif ication

IEC61400-12-1 standard on power performance measurements, annex I:Influence parameters for classification

Influence parameter ranges (based on 10min averages) of Classes A and B

Class ATerrain meets requirements

of flat site

Class BTerrain does not meet

requirements of flat siteMin Max Min Max

Wind speed range to cover [m/s] 4 16 4 16Turbulence intensity 0,03 0,12+0,48/V 0,03 0,12+0,96/V

Turbulence structure u/v/w 1/0,8/0,5(non-isotropic turbulence)

1/1/1(isotropic turbulence)

Air temp. [C] 0 40 -10 40

Air density [kg/m3] 0,9 1,35 0,9 1,35

Average flow inclination angle [] -3 3 -15 15For assessment of a class using simulation it is suggested the wind spectrum is a Kaimal wind spectrum witha longitudinal turbulence length scale of 350m



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IEC61400-12-1 standard on power performance measurements, Annex J:Classification procedure with the use of general time domain model

Realcup-anemometer

-friction-torque curves-inertia-angular char.

Cup-anemometer

model

Calibrations

Fitting to

cup-anem.

model

Calculation

of responses

Classification

index

Class

Environmental

operational

conditions




57/70



A systematic analysis of deviations from the calibration line due to influence

parameters using artificially generated 3D wind and general time domainmodel

-0,4

-0,3

-0,2

-0,1

0

0,1

0,2

0,3

0,4

0 2 4 6 8 10 12 14 16 18 20

Wind Speed [m/s]

Deviations[m/s]

Class 1Class 2Deviations

Example of deviations of a Class 2.0A cup anemometer




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IEC61400-12-1, Annex IClass selection of cup anemometers

The selection of an anemometer class for a specific measurement depends on the terrain or the accuracythat is needed for the measurement.

Class A: Associated to flat terrain, and with general influence parameter ranges for this type ofterrain.

Class B: Associated to terrain that does not meet the requirements of flat terrain, and with generalinfluence parameter ranges for complex terrain.

Class S: Associated to a specified accuracy, where the influence parameter ranges are restricted toallow for the specified accuracy of the anemometer. Alternatively the class may beassociated to influence parameter ranges that are not specifically covered by class A or

class B or to influence parameter ranges that are verified during the power performancemeasurements.




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IEC61400-12-1, Annex IClass description of cup anemometers

The class number k shall be determined as the maximum anemometer response deviation (from thehorizontal wind speed input) in the wind speed range corresponding to the formula:

5 / 0,5

100 max /

i i

i i

w m s U

k w

= +

=

where iw is a weighting function that defines the deviation envelope

max,i is the maximum deviation for any wind speed bin i in the wind speed range in m/s

k is the class number

The classification of an anemometer is specified by the class number k and the class type by kA and kB or

kS, for example 1,7A and 2,5S.




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IEC61400-12-1, Annex I

Classification of cup anemometersACCUWIND project results

Classification IEC61400-12-1

Model: General time domain +FOI tilt responseHorizontalwsp definition

Vectorwsp definition

Cup anemometer Class A Class B Class A Class BNRG max 40 2.4 8.3 2.7 3.0Ris P2546 1.4 5.1 1.7 9.2

Thies FC 1.8 3.8 1.6 4.4Vaisala WAA151 2.2 11.9 1.7 6.1Vector L100 1.8 4.5 1.6 4.0




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IEC61400-12-1, Annex IClassification of cup anemometersACCUWIND project results

Classification IEC61400-12-1Model: General time domain +DEWI tilt response

Horizontalwsp definition

Vectorwsp definition

Cup anemometer Class A Class B Class A Class BNRG max 40 2.4 7.7 2.8 4.8Ris P2546 1.9 8.0 2.4 12.0

Thies FC 1.5 2.9 1.9 6.3Vaisala WAA151 1.7 11.1 1.2 5.5Vector L100 1.8 4.5 1.7 4.0




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Mast and boom flow distortionIEC61400-12-1 standard on power performance measurements

Annex G Requirements for top mounting, one anemometer

Vertical tube

Mast top

Mast shall be within 1:5 cone(mast centre to cone relative

to vertical distance to anemometer)

Hub height relativeto ground at met mast

Minimum 0,75m

Minimum 1,5mNo flow disturbances alowedabove this line

No other instruments on boomsabove this line



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Annex G Requirements for top mounting, two anemometers

Minimum 15 timesboom diameterRecommended 25 timesboom diameter

Minimum 1,5m and maximum 2,5m


Minimum 1,5m

Minimum 0,75m

No flow disturbances alowedabove this line

No other instruments on boomabove this line

Mast top

Mast box with pressure sensor



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Vertical tube

Mast top

mast within 1:5 cone(mast centre to cone relative

to vertical distance to anemometer)


Free tubeMinimum 0,75m

Minimum 1,5m andMaximum 2,5m

Boom


Tmp Control anemometer should be mountedas described in clause G.5


Annex G Requirements for top mounting, other sensors



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Minimum 1,5m and maximum 2,5m


Minimum 1,5m and

maximum 10% of hub height

Minimum 0,75m


Mast top

Minimum 15 times

boom diameterRecommended 25 timesboom diameter

Boom


Annex G Requirements for top mounting, other sensors



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6 00 Sp C p


0,960

0,965

0,970

0,975

0,980

0,985

0,990

0,995

1,000

2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0 6,5 7,0 7,5 8,0 8,5 9,0 9,5 10,0

Distance to Center Divided by Mast Diameter R/d

CentrelineRelativeWindSpeed

Mast and boom flow distortion

IEC61400-12-1 standard on power performance measurementsAnnex G Flow distortion round a tubular mast



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p p


L

R

Actuator disc

d

Three legged mastCentrelinewind speed deficit U

0,960

0,965

0,970

0,975

0,980

0,985

0,990

0,995

1,000

2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0 6,5 7,0 7,5 8,0 8,5 9,0 9,5 10,0

Distance to Mast Centre Divided by Mast Leg Distance R/L

CentrelineRelativeWindSpeed

Ct=0,1

Ct=0,3

Ct=0,5

Ct=0,7

Tubular (based on R/d)

Mast and boom flow distortion

IEC61400-12-1 standard on power performance measurementsAnnex G Flow distortion round a three-legged mast



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p p


Other inf luence factors on cup anemometers

Rime Ice Dust Bird shit

Example: shit from cormorant



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p p


Other inf luence factors on cup anemometersExample of influence of rime on a 116m mast:

J umps in wind speed from about 7.5m/s to 12.5m/s at 60m, 80m and100m levels

-3

-2

-1

0

1

2

3

4

5

6

7

8

9

1011

12

13

14

15

16

1 37 73 109 145 181 217 253 289 325 361 397 433 469 505

10-min periods

Measure

dwindspeed[m/s]ortemperature[degC

Wsp 116m

Wsp 100m

Wsp 80m

Wsp 60m

Tmp 60m



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p p

Other influence factors on cup anemometersIcing (re. Vaisala)

Documents

DTU Wind Speed Course Cups