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