Quantifying Turbulence for Tidal Power Applications
Quantifying Turbulence for Tidal Power Applications J. Thomson1, M. Richmond2, B. Polagye1, V. Durgesh2 1
U. of Washington - Northwest National Marine Renewable Energy Center 2 Pacific Northwest National Laboratory – Hydrology Group
IEEE/MTS Oceans Conference 21 September 2010
NNMREC
Mo#va#on Turbine performance Turbine fatigue Environmental effects
NNMREC
Objec#ves Field measurements from an actual tidal power site Evaluation of metrics: Turbulent intensity, I = σv /
Turbine site Port Townsend
Turbulent dissipation rate, ε Coherence,
Best practices: Sampling schemes Rigorous treatment of errors
NNMREC
Instruments and sampling Acoustic Doppler
Current Profiler (ADCP): volume sampling
** beam coordinates**
64 s @ 2 Hz= 128 points,
every 30 min
ADV mount Accelerometer mount CTD mount ADCP mount Ballast (1500 lbs)
Acoustic Doppler
Velocimeter (ADV): point precision 64 s @ 32 Hz = 2048 pts,
every 10 min
5 m tripod deployed in 22 m water depth
NNMREC
Mean veloci#es
m
v,c
[m/s]
[m/s]
ADCP (Acoustic Doppler Current Profiler)
1.5 1 0
ADV (Acoustic Doppler Velocimeter) ADCP 4.6 m above seabed
05/07
05/14
0.2 0.1 0
NNMREC
Raw velocity fluctua#ons [m/s] 1.600 1.440 0.25 1.280
ADCP mv [m/s]
0.2
1.120 0.960
0.15
Raw ADCP data is noisy! 0.1
0.05
0.800 0.640
Corrected velocity std deviation is σv,c = √(σv2 – n2)
0.480 0.320
0 0
0.05
0.1
0.15 0.2 ADV mv [m/s]
0.25
0.3
0.160
NNMREC
mv,c [m/s]
[m/s]
Corrected results 1.5 1 0
ADV ADCP
05/07
05/14
05/07
05/14
0.2 0.1 0
Ic [%]
50 25
¡ [W/m3]
0
I ≈ 10% 05/07
05/14
ï1
10
ï3
10
NNMREC
ï6
10
05/07
05/14
ADV ADCP
1.5 1 0
05/07
05/14
0.2 06ïMayï2010 01:30
0.1 0
m/s
mv,c [m/s]
[m/s]
Sta#onarity (stable mean)
Vx
0
Vz
100 80 short, 60 0
cor
25but not too Short, 0
Vy
05/07 ï1 0
50 Ic [%]
1
05/14 10
20
10
20
05/07
ï3
10
snr
3
W/m ]
ï1
40
50
60
30
40
50
60
70
05/14
NNMREC
100 50 0
70
records (“bursts”) are necessary for robust statistics… …see Polagye et al (in prep)
150
10
30
10
20
30 40 Time [s]
50
60
70
• Frequency spectra from ADV
Dissipa#on rate
• Inertial sub-range shows cascade of energy to small scales, • Slope is rate of energy loss
06ïMayï2010 01:30
ï2
10
Vx Vy Vz
ï3
2 2
S [m /s /Hz]
10
ï4
horizontal noise
10
ï5
fï5/3
10
vertical noise Inertial sub-range
ï6
10
ï2
10
ï1
10
0
10 f [Hz]
1
10
2
10
NNMREC
Dissipa#on rate
• Spatial structure from ADCP • Inertial sub-range shows cascade of energy to small scales, • Slope is rate of energy loss
06ïMayï2010 01:30:00, z = 4.71 m, v = 0.8 m/s 0.05 0.045
Inertial sub-range
0.04
D(z,r) [m2/s2]
0.035 0.03 0.025 0.02 0.015
noise (along beam)
0.01
beam beam beam beam
0.005 0 0
5
10
15
20
1 2 3 4 25
r [m]
NNMREC
mv,c [m/s]
[m/s]
Combined results 1.5 1 0
ADV ADCP
05/07
05/14
05/07
05/14
05/07
05/14
05/07
05/14
0.2 0.1 0
Ic [%]
50 25
¡ [W/m3]
0 ï1
10
ï3
10
ï6
10
NNMREC
Height [m]
Ver#cal dependence ADCP 20 ADV
20
20
18
18
18
18
16
16
16
16
14
14
14
14
12
12
12
12
10
10
10
10
8
8
8
8
6
6
6
6
4
4
4
4
2
2
2
2
0 0 0.5 1 1.5 [m/s]
0 0
0.1 0.2 mv,c [m/s]
0 0
20
5
10 I [%] c
0 ï2 ï1.5 ï13 log10(¡) [W/m ]
NNMREC
Freq [hz]
Coherent Turbulent Kine#c Energy (eddies) 26.00 5.20 2.89 2.00 1.53 1.24 1.04 0.90 0.79 0.70 0.63 0.58 0.53 0.49 0.46 0.43 0.40 0.38 0.36 0.34
6.25
12.50
18.75
25.00
31.25
37.50
43.75
50.00
56.25
62.50
Time [s]
NNMREC
Conclusions
ADV I c ADCP I c 50
burst
40
30
20
Turbulent intensity ≈ 10%
10
0 0
5
10 %
15
20
Doppler measurement error (“noise”) can heavily bias
observed velocity variance and must be removed. Dissipation rate has more dynamic range the turbulent
intensity, but operational significance unknown
Coherent TKE shows time-‐space scales of eddies
NNMREC
Acknowledgments Funding provided by the U.S.
Department of Energy, Office of Energy Efficiency and Renewable Energy -‐ Wind and Water Power Program.
Tripod assembly and deployment:
Joe Talbert (UW-‐APL)
Boat ops: Capt. Andy Reay-‐Ellers,
Alex deKlerk (UW-‐APL)
NNMREC
Tripod mo#on? 04ïMayï2010
1.5 0.2
v [m/s]
Acceleration [g]
0.4
1 0.5
0 12:00
15:00
0 18:00
NNMREC
U. of Washington - Northwest National Marine Renewable Energy Center 2 Pacific Northwest National Laboratory – Hydrology Group
IEEE/MTS Oceans Conference 21 September 2010
NNMREC
Mo#va#on Turbine performance Turbine fatigue Environmental effects
NNMREC
Objec#ves Field measurements from an actual tidal power site Evaluation of metrics: Turbulent intensity, I = σv /
Turbine site Port Townsend
Turbulent dissipation rate, ε Coherence,
Best practices: Sampling schemes Rigorous treatment of errors
NNMREC
Instruments and sampling Acoustic Doppler
Current Profiler (ADCP): volume sampling
** beam coordinates**
64 s @ 2 Hz= 128 points,
every 30 min
ADV mount Accelerometer mount CTD mount ADCP mount Ballast (1500 lbs)
Acoustic Doppler
Velocimeter (ADV): point precision 64 s @ 32 Hz = 2048 pts,
every 10 min
5 m tripod deployed in 22 m water depth
NNMREC
Mean veloci#es
m
v,c
[m/s]
[m/s]
ADCP (Acoustic Doppler Current Profiler)
1.5 1 0
ADV (Acoustic Doppler Velocimeter) ADCP 4.6 m above seabed
05/07
05/14
0.2 0.1 0
NNMREC
Raw velocity fluctua#ons [m/s] 1.600 1.440 0.25 1.280
ADCP mv [m/s]
0.2
1.120 0.960
0.15
Raw ADCP data is noisy! 0.1
0.05
0.800 0.640
Corrected velocity std deviation is σv,c = √(σv2 – n2)
0.480 0.320
0 0
0.05
0.1
0.15 0.2 ADV mv [m/s]
0.25
0.3
0.160
NNMREC
mv,c [m/s]
[m/s]
Corrected results 1.5 1 0
ADV ADCP
05/07
05/14
05/07
05/14
0.2 0.1 0
Ic [%]
50 25
¡ [W/m3]
0
I ≈ 10% 05/07
05/14
ï1
10
ï3
10
NNMREC
ï6
10
05/07
05/14
ADV ADCP
1.5 1 0
05/07
05/14
0.2 06ïMayï2010 01:30
0.1 0
m/s
mv,c [m/s]
[m/s]
Sta#onarity (stable mean)
Vx
0
Vz
100 80 short, 60 0
cor
25but not too Short, 0
Vy
05/07 ï1 0
50 Ic [%]
1
05/14 10
20
10
20
05/07
ï3
10
snr
3
W/m ]
ï1
40
50
60
30
40
50
60
70
05/14
NNMREC
100 50 0
70
records (“bursts”) are necessary for robust statistics… …see Polagye et al (in prep)
150
10
30
10
20
30 40 Time [s]
50
60
70
• Frequency spectra from ADV
Dissipa#on rate
• Inertial sub-range shows cascade of energy to small scales, • Slope is rate of energy loss
06ïMayï2010 01:30
ï2
10
Vx Vy Vz
ï3
2 2
S [m /s /Hz]
10
ï4
horizontal noise
10
ï5
fï5/3
10
vertical noise Inertial sub-range
ï6
10
ï2
10
ï1
10
0
10 f [Hz]
1
10
2
10
NNMREC
Dissipa#on rate
• Spatial structure from ADCP • Inertial sub-range shows cascade of energy to small scales, • Slope is rate of energy loss
06ïMayï2010 01:30:00, z = 4.71 m, v = 0.8 m/s 0.05 0.045
Inertial sub-range
0.04
D(z,r) [m2/s2]
0.035 0.03 0.025 0.02 0.015
noise (along beam)
0.01
beam beam beam beam
0.005 0 0
5
10
15
20
1 2 3 4 25
r [m]
NNMREC
mv,c [m/s]
[m/s]
Combined results 1.5 1 0
ADV ADCP
05/07
05/14
05/07
05/14
05/07
05/14
05/07
05/14
0.2 0.1 0
Ic [%]
50 25
¡ [W/m3]
0 ï1
10
ï3
10
ï6
10
NNMREC
Height [m]
Ver#cal dependence ADCP 20 ADV
20
20
18
18
18
18
16
16
16
16
14
14
14
14
12
12
12
12
10
10
10
10
8
8
8
8
6
6
6
6
4
4
4
4
2
2
2
2
0 0 0.5 1 1.5 [m/s]
0 0
0.1 0.2 mv,c [m/s]
0 0
20
5
10 I [%] c
0 ï2 ï1.5 ï13 log10(¡) [W/m ]
NNMREC
Freq [hz]
Coherent Turbulent Kine#c Energy (eddies) 26.00 5.20 2.89 2.00 1.53 1.24 1.04 0.90 0.79 0.70 0.63 0.58 0.53 0.49 0.46 0.43 0.40 0.38 0.36 0.34
6.25
12.50
18.75
25.00
31.25
37.50
43.75
50.00
56.25
62.50
Time [s]
NNMREC
Conclusions
ADV I c ADCP I c 50
burst
40
30
20
Turbulent intensity ≈ 10%
10
0 0
5
10 %
15
20
Doppler measurement error (“noise”) can heavily bias
observed velocity variance and must be removed. Dissipation rate has more dynamic range the turbulent
intensity, but operational significance unknown
Coherent TKE shows time-‐space scales of eddies
NNMREC
Acknowledgments Funding provided by the U.S.
Department of Energy, Office of Energy Efficiency and Renewable Energy -‐ Wind and Water Power Program.
Tripod assembly and deployment:
Joe Talbert (UW-‐APL)
Boat ops: Capt. Andy Reay-‐Ellers,
Alex deKlerk (UW-‐APL)
NNMREC
Tripod mo#on? 04ïMayï2010
1.5 0.2
v [m/s]
Acceleration [g]
0.4
1 0.5
0 12:00
15:00
0 18:00
NNMREC
