Dave Corbus, Dan Prascher

Presentation at the 24th ASME Wind Energy Symposium

January 10-13, 2005

Analysis and Comparison of Test Results from the Small Wind Research

Turbine (SWRT) Test Project

2SWRT Project

SWRT Test Background

• SWRT Test

•Supply data for model validation of small furling wind turbines

•Increase understanding of furling and small wind turbine dynamics

•Further state-of-the-art test procedures for small wind turbines

3.51"3.30"3.72"

3SWRT Project

SWRT Testing and Model Development• SWRT Test

•Three different turbine configurations tested

• Most comprehensive small turbine test

• Upgrade FAST model to include furling

•Perform model comparisons between SWRT FAST and ADAMS models and FAST and SWRT

• Models often break down more for small turbine conditions

•In and out of stall more

•More yawed flow conditions

•Dynamically active turbine

4SWRT Project

SWRT Test Description

Yaw slip rings and encoder

Furl Sensor

Sonic anemometer junction box

Shaft sensor

Flap and edge blade strain gages

Tower leg load cell “washers”

Rotor slip ring, encoder, and amplifiers

5SWRT Project

SWRT shaft sensor - first accurate small turbine thrust

measurements

6SWRT Project

Shaft Sensor

Measures Shaft 0/90 bending, torque, thrust on fixed frame

4 by 4 cross-talk matrix

Critical path load is the shaft bending from gyroscopic loads– During high yaw

rate events and high rpm

7SWRT Project

Pre-testing Turbine Characterization

Data for modeling included:

– Tail assembly and main frame:

• Weight, Cg, bi-filar, moment of inertia about yaw axis

– Magnet can Cg and moment of inertia

– Tail damper properties– Exact turbine

geometries– Blade modal test

8SWRT Project

Data Analysis – Edge Correction

3 edge summation in-plane did not equal torque – About 3-5x higher due

to centrifugal loading!

• But slow rolls validate calibrations

– Moment arm created• Blade Cg minus

centerline of rotation

• Difference in edge gage neutral axis and blade Cg

Rotor RPM

rad/sec

(rad/s)^2

centrifugal force (N)

edge bending- 1.4" offset (N-m)

0 0 0 0 040 4 18 307 -580 8 70 1228 -19

120 13 158 2764 -43160 17 281 4913 -77200 21 438 7677 -120240 25 631 11054 -173280 29 859 15046 -236320 34 1123 19652 -308360 38 1421 24872 -390400 42 1754 30706 -481

9SWRT Project

Moment Arm for Edge Correction

Leading Edge

Center of Rotation

Center of Gravity

Planar Center Line

Trailing Edge

LOFF

MCentrip

FB

MCentrip = LOFF FB cos

10SWRT Project

Edge Corrected by Unloaded Correlation

R2 = 0.9986

R2 = 0.9989

0.00

0.20

0.40

0.60

0.80

1.00

0 40000 80000 120000 160000omega ^2 (RPM^2)

Bla

de

Ed

ge

Ben

din

g,

volt

s

Mean Blade 3 Mean Blade 1Linear (Mean Blade 1) Linear (Mean Blade 3)

11SWRT Project

Max and Mean Furl vs. Mean Wind Speed

-20

0

20

40

60

80

5 10 15 20

Mean Wind Speed, m/s

Fu

rl, d

eg

Max Furl Furl

12SWRT Project

Yaw Rate vs. Mean Wind Speed

-150

-100

-50

0

50

100

150

5 10 15 20

Mean Wind Speed, m/s

Ya

w R

ate

, de

g/s

Max yaw rate Mean yaw rate Min yaw rate

13SWRT Project

Electrical Power vs. Mean Wind Speed

0

2

4

6

8

10

12

14

5 10 15 20Mean Windspeed, m/s

Me

an

Ele

ctr

ic P

ow

er,

kW

Max Power Mean Power Min Power

14SWRT Project

Rotor Speed vs. Mean Wind Speed

0

100

200

300

400

500

600

5 10 15 20Mean Windspeed, m/s

RP

M

RPM mean RPM max RPM min

15SWRT Project

Thrust vs. Mean Wind Speed

-2000

0

2000

4000

6000

5 10 15 20

Mean Windspeed, m/s

Th

rus

t, N

.

Max Mean Min

16SWRT Project

Furl vs. Thrust

0

10

20

30

0 500 1000 1500 2000 2500

Thrust, N

Fu

rl,

de

g

Mean Furl versus Thrust

17SWRT Project

SWRT Furling Event – Time Series Plot

320320 340340 360360 380380 400400 4204200

10

20

30

40-1000

0

1000

2000

3000

4000

150

200

250

300

350

400

450

Win

d S

pee

d &

Fu

rl A

ng

le

Time, seconds

Sh

aft

Th

rust

Ro

tor

RP

M

320 340 360 380 400 420

-60

-30

0

30

60

90Y

aw E

rro

r

18SWRT Project

Furling and Center of Thrust

0

5

10

15

20

25

30

35

40

45

50

5 7 9 11 13 15 17 19 21

Time, seconds

Fu

rl, Y

aw E

rro

r (d

egre

es)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

Cen

ter

of

Th

rust

(m

eter

s)

furl yaw error center of thrust

19SWRT Project

SWRT Test Configurations

All configurations tested with inverter load – Total of 514 10-minute

records

A few resistor load files taken for each configuration– Some scatter in rpm-

torque curve from inverter controller hysteresis

SWRT Configuration

A B C

Airfoil SH3052 SH3052 SH3055

Lateral shim

4 degree

none none

Swept Area/Rotor Diameter

26.4 m2/ 5.8

m

26.4 m2/ 5.8

m

35.3m2 /

6.7 m

Blade pitch

11.5 11.5 9.5

20SWRT Project

Furl vs. Wind Speed for Different Configurations

0

5

10

15

20

25

30

35

40

45

50

9 11 13 15 17 19 21

Mean Windspeed, m/s

Fu

rl D

eg

ree

s

Mean Config A

Mean Config B

Mean Config C

Poly. (MeanConfig C)Poly. (MeanConfig A)Poly. (MeanConfig B)

Configuration C

Configuration B

Configuration A

21SWRT Project

Thrust vs. Wind Speed for Different Configurations

0

500

1000

1500

2000

2500

3000

3500

5 9 13 17 21Mean Windspeed, m/s

Th

rus

t, N

Mean Config AMean Config BMean Config C

22SWRT Project

Ratio of Tail/Met Wind Speed vs. Wind Speed

0%

20%

40%

60%

80%

100%

5 10 15 20Wind Speed, m/s

Ra

tio

Ta

il/M

et

WS

, %

Tail/Met WS Ratio A

Tail/Met WS Ratio C

23SWRT Project

Power/Thrust Ratio for Configurations A and C

0

1

2

3

4

5

6

5 10 15 20Wind Speed, m/s

Po

we

r/T

hru

st

Ra

tio

Power/Thrust Ratio Config C

Power/Thrust Ratio Config A

24SWRT Project

Power vs. Wind Speed for Configuration

A and C

0

2

4

6

8

10

12

5 10 15 20

Mean Windspeed, m/s

Me

an

Ele

ctr

ic P

ow

er,

kW

Mean Config A

Mean Config C

25SWRT Project

Shaft tilt moment vs. wind speed for different configurations

-600

-500

-400

-300

-200

-100

0

100

5 10 15 20

Mean Windspeed, m/s

Sh

aft

Tilt

Be

nd

ing

, N-m

Mean Config A

Mean Config B

Mean Config C

26SWRT Project

Shaft yaw moment vs. wind speed for different configurations

-250

-200

-150

-100

-50

0

5 10 15 20Mean Windspeed, m/s

Sh

aft

Ya

w B

en

din

g, N

-m

Mean Config CMean Config AMean Config B

27SWRT Project

Furling and Inflow

Use sonic anemometer and meteorological data

Correlate inflow parameters and furling

Shows significance of vertical wind component and coherent turbulent kinetic energy

28SWRT Project

Furling and Richardson Number

SWRT Configuration "A" Mean Furling Angle & Mean Coherent Turbulent Kinetic Energy (Coh TKE)

vs Vertical Stability (Ri)

2-50m layer Richardson number stability parameter, Ri

-0.15 -0.10 -0.05 0.00 0.05 0.10 0.15

Meanfurling angle (deg)

0.001

0.01

0.1

1

10

100

Hub mean Coh TKE

(m2/s2)

0

10

20

30

40

50

60

Mean Furling AngleMean Coh TKE

Max ART Response

29SWRT Project

- CoTKE and vertical gust variance for two files with same wind

speed and different furl

Cycles/min0.1 1 10 100

RM

S C

oh

TK

E (

m2/s

2)

0

2

4

6

8

10

12

Coherent TKE

Frequency (Hz)0.001 0.01 0.1 1 10

RM

S C

oh

TK

E (

m2/s

2)

0

2

4

6

8

10

12

FurlNo Furl

Wavelength in Rotor Diameters

1 10 100 1000

RM

S C

oh

TK

E (

m2/s

2)

0

2

4

6

8

10

12

Vertical Gust Velocity Variance

Frequency (Hz)

0.001 0.01 0.1 1 10

w' V

aria

nce

Sp

ectr

a (m

2/s

2)

0.0

0.1

0.2

0.3

0.4

0.5

Wavelength in Rotor Diameters

1 10 100 1000

w' V

aria

nce

Sp

ectr

a (m

2/s

2)

0.0

0.1

0.2

0.3

0.4

0.5

Cycles/min0.1 1 10 100

w' V

aria

nce

Sp

ectr

a (m

2/s

2)

0.0

0.1

0.2

0.3

0.4

0.5

30SWRT Project

SWRT Summary

Most comprehensive small turbine test data set

Better understanding of small wind turbine dynamic behavior, including thrust and furling

SWRT test data and modeling effort will help make furling design efforts for small wind turbines easier, but furling remains a challenge!

Better test procedures for small turbine testing

Inflow analysis shows effects of turbulence

Data will be available on NREL Website and final technical report available soon

SWRT FAST modeling results presented tomorrow morning