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# Wind energy II. Lesson 2. Wind speed measurement

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### Wind energy II. Lesson 2. Wind speed measurement

1. 1. Wind Energy I Wind speed measurementsMichael Hölling, WS 2010/2011 slide 1
2. 2. Wind Energy I Class content 5 Wind turbines in 6 Wind - blades general 2 Wind measurements interaction 7 Π-theorem 8 Wind turbine characterization 3 Wind field 9 Control strategies characterization 10 Generator 4 Wind power 11 Electrics / gridMichael Hölling, WS 2010/2011 slide 2
3. 3. Wind Energy I 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 anemometerMichael Hölling, WS 2010/2011 slide 3
4. 4. Wind Energy I Sensor resolution Temporal and spatial resolution Taylor’s hypothesis - picture of frozen turbulence: “Eddies have much longer life-time than they need to travel past a sensor” σu << 1 u temporal resolution limits spatial resolution AND spatial resolution limits temporal resolutionMichael Hölling, WS 2010/2011 slide 4
5. 5. Wind Energy I Pressure measurements Why should we measure the pressure ? Bernoulli equation: ptotal = pdyn + pstatic with: pdyn = 1/2 · ρair · u 2 Prandtl tubeMichael Hölling, WS 2010/2011 slide 5
6. 6. Wind Energy I Pressure measurements Therefore the velocity is Measure the pressure e.g. with given by: an “inclined tube manometer” 2 · (ptotal − pstatic ) u= ρairMichael Hölling, WS 2010/2011 slide 6
7. 7. Wind Energy I Cup anemometry Why this basic design ? u urotMichael Hölling, WS 2010/2011 slide 7
8. 8. Wind Energy I Cup anemometry Different modelsMichael Hölling, WS 2010/2011 slide 8
9. 9. Wind Energy I Cup anemometry Calibration 5 4 u [m/s] 3U [V] U[V] 2 1 0 0 1000 2000 3000 4000 5000 f [Hz] t t[s] [s] optoelectronic detection inductive detectionMichael Hölling, WS 2010/2011 slide 9
10. 10. Wind Energy I Cup anemometry Over-speeding gusts at 2/3 Hz, 9 m/s v [m/s]u [m/s] t [s] measured turbulence intensity 33% 8% hot-wire anemometer cup anemometer Michael Hölling, WS 2010/2011 slide 10
11. 11. Wind Energy I Cup anemometry Inclined flow tilt response anemometer Type 3.3351.00.000 , serial 0807011 at ca. 10 m/s dataset 1796_09 0,1 nozzle 0,08 0,06 -20° 0,04 nozzle rel. deviation of anemoemter frequency 0,02 0 +20° -0,02 -0,04 -0,06 -0,08 -0,1 -0,12 -0,14 -0,16 -0,18 -0,2 -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 tilt angle /° dev. V anemo at 1Hz dev. V anemo bin averageMichael Hölling, WS 2010/2011 slide 11
12. 12. Wind Energy I 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.comMichael Hölling, WS 2010/2011 slide 12
13. 13. Wind Energy I Ultrasonic anemometry Measurement principleMichael Hölling, WS 2010/2011 slide 13
14. 14. Wind Energy I Ultrasonic anemometry Different models - 2D and 3DMichael Hölling, WS 2010/2011 slide 14
15. 15. Wind Energy I Ultrasonic anemometry Drawbacks Deviation from horizontal velocityu supports create wakes system is expensiveMichael Hölling, WS 2010/2011 slide 15
16. 16. Wind Energy I LiDAR Measurement principleMichael Hölling, WS 2010/2011 slide 16
17. 17. Wind Energy I LiDAR Possibilities with LiDARMichael Hölling, WS 2010/2011 slide 17
18. 18. Wind Energy I 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 frequencyMichael Hölling, WS 2010/2011 slide 18
19. 19. Wind Energy I Sphere anemometer Measurement principle deﬂection of a ﬂexible tube due to drag forces acting l3 Fs Ft s= · + E·J 3 8 with general expression for drag force 1 F = · · A · cD · v 2 2 drag coefﬁcient cD considered constant for Re ≈ 103 . . . 2 · 105 leads to √ s∝v ⇒v =m· 2 s Easy calibration function!Michael Hölling, WS 2010/2011 slide 19
20. 20. Wind Energy I Sphere anemometer Measurement principle deﬂection of a ﬂexible tube due to drag forces acting l3 Fs Ft s= · + Kugel sphere E·J 3 8 with general expression for drag force laser Laser 1 F = · · A · cD · v 2 Rohr l 2 drag coefﬁcient cD considered constant for tube Re ≈ 103 . . . 2 · 105 leads to Gewinde √ s∝v ⇒v =m· 2 s 2D-PSD Easy calibration function!Michael Hölling, WS 2010/2011 slide 19
21. 21. Wind Energy I Sphere anemometer Calibration 270° v [m/s] 0.3 20 0.2 17 0.1 14 Ux [V] 0.0 0° 180° 11 9 –0.1 7 –0.2 ! 5 3 2 –0.3 1 90° 0 –0.3 –0.2 –0.1 0.0 0.1 0.2 0.3 Uy [V]Michael Hölling, WS 2010/2011 slide 20
22. 22. Wind Energy I Sphere anemometer Gusts measurementsMichael Hölling, WS 2010/2011 slide 21
23. 23. Wind Energy I Sphere anemometer Comparison of time series u [m/s] t [s] measured turbulence intensities 33% 32% 8% hot-wire anemometer sphere cup anemometerMichael Hölling, WS 2010/2011 slide 22
24. 24. Wind Energy I Sphere anemometer Comparison of power spectraMichael Hölling, WS 2010/2011 slide 23
25. 25. Wind Energy I Sphere anemometer “Evolution” of sphere anemometer 2007 2008 2009 2010Michael Hölling, WS 2010/2011 slide 24