2. The VAWT in Skew: Stereo-PIV and Vortex Modeling ir. C.J. Sim ã o Ferreira, M.Sc. K. Dixon, Dipl.-Ing. C. Hofemann, Prof. Dr. ir. G.J.W. van Bussel, Prof. Dr. ir. G. A.M. van Kuik 47th AIAA Aerospace Sciences Meeting 5 - 8 Jan 2009, Orlando World Center Marriott Orlando, Florida

3. The VAWT in Skew: Stereo-PIV and Vortex Modeling 3 Who What Why How Where Results Carlos, Kristian, Claudia,... Numerical & Experimental… Effect of the skewed angle on wake Upwind & Downwind blade passage To understand the influence of the skew angle on the performance of the VAWT Vertical Axis Wind Turbine (VAWT) Table of contents

4. The VAWT in Skew: Stereo-PIV and Vortex Modeling 4 What ? VAWT

5. The VAWT in Skew: Stereo-PIV and Vortex Modeling 5 Skewed flow -> Misalignment of the flow perpendicular to the ground What VAWT in Skew

6. The VAWT in Skew: Stereo-PIV and Vortex Modeling Why ? VAWT operating under skewed flow show a higher efficiency than VAWT operating under normal conditions ! Why ?

7. The VAWT in Skew: Stereo-PIV and Vortex Modeling How ?Numerical 3D unsteady free wake panel method Design and research tool –capturing the 3D nature of a VAWT and its wake Allows to analyze the effect of skew in terms of –bound circulation, –shed and trailing vorticity –torque, wake and flow asymmetry Validated by PIV and Smoke Trail Studies

8. The VAWT in Skew: Stereo-PIV and Vortex Modeling 8 How ? Numerical

9. The VAWT in Skew: Stereo-PIV and Vortex Modeling 9 Two blades: NACA 0015 (trailing edge) NACA 0018 (quarter chord) Tip speed ratio: λ = 4 Wind speed: 10 m/s Reynolds number: 8 x 10 4 How ?Experimental l = 700 mm Z X Y d= 570 mm c = 60 mm λ = ωR/V

10. The VAWT in Skew: Stereo-PIV and Vortex Modeling 10 Wind Y X Z How ? Low speed / Low turbulence Wind Tunnel

11. The VAWT in Skew: Stereo-PIV and Vortex Modeling How ? 3D-Stereo-PIV

12. The VAWT in Skew: Stereo-PIV and Vortex Modeling 12 Where ?Upwind & Downwind X Y 0°0° 90° 180° measuring planes wind -120 mm -0.42 y/R 120 mm 0.42 y/R upwinddownwind NumericalUpwind & Downwind Experimental Downwind

13. The VAWT in Skew: Stereo-PIV and Vortex Modeling 13 Results ?Tip vortex locus (Exp.) Skew angles:  = +20   = 0  = - 20 

14. The VAWT in Skew: Stereo-PIV and Vortex Modeling 14 Results ?Tip vortex locus (Sim.) Skew angles:  = +20   = 0  = - 20 

15. The VAWT in Skew: Stereo-PIV and Vortex Modeling 15 Results ?Tip vortex locus

16. The VAWT in Skew: Stereo-PIV and Vortex Modeling 16 Results ?Location of the wake Azimuth angle:  = 90  Skew angles:  = +20   = 0   = - 20 

17. The VAWT in Skew: Stereo-PIV and Vortex Modeling 17 Results ?Trailing vorticity Skew angles:  = +20   = 0   = - 20 

18. The VAWT in Skew: Stereo-PIV and Vortex Modeling 18 Results ?Shed vorticity Skew angles:  = +20   = 0   = - 20 

19. The VAWT in Skew: Stereo-PIV and Vortex Modeling 19 Results ?Bound vorticity Skew angles:  = +20   = 0   = - 20 

20. The VAWT in Skew: Stereo-PIV and Vortex Modeling 20 Results ?Normal Force Skew angles:  = +20   = 0 

21. The VAWT in Skew: Stereo-PIV and Vortex Modeling 21 Results ?Trailing vorticity Skew angles:  = 0   = 10   = 20   = 30 

22. The VAWT in Skew: Stereo-PIV and Vortex Modeling 22 Results ?Shed vorticity Skew angles:  = 0   = 10   = 20   = 30 

23. The VAWT in Skew: Stereo-PIV and Vortex Modeling 23 Results ?Tangential Force Skew angles:  = 0   = 10   = 20   = 30 

24. The VAWT in Skew: Stereo-PIV and Vortex Modeling 24 Results ?Validation

25. The VAWT in Skew: Stereo-PIV and Vortex Modeling 25 Conclusions ? The impact of the skew angle on the wake has been shown by the 3D panel method Skewed flow –increases the performance of the VAWT –generates an asymmetry of the wake in z-direction –causes asymmetry of the expansion of the wake in y-direction 3D unsteady free wake panel code –is able to replicate the effect of skew –shows the impact of the skew angle on the strength of the wake for trailing and shed vorticity –shows the effect on bound vorticty as well as on normal and tangential forces –is not able to capture the roll of motion

26. The VAWT in Skew: Stereo-PIV and Vortex Modeling Questions ? 26

27. The VAWT in Skew: Stereo-PIV and Vortex Modeling 27 Results ?Induction in x-direction Skew angles:  = +20   = 0   = - 20 

28. The VAWT in Skew: Stereo-PIV and Vortex Modeling 28 Results ?Induction in z-direction Skew angles:  = +20   = 0   = - 20 

29. The VAWT in Skew: Stereo-PIV and Vortex Modeling 29 Why ?

30. The VAWT in Skew: Stereo-PIV and Vortex Modeling Δt 30 How ? Stereo PIV / Displacement

31. The VAWT in Skew: Stereo-PIV and Vortex Modeling 31 NACA 0018: leading edge quarter chord NACA 0015: flat tip trailing edge What ? Blade configuration

32. The VAWT in Skew: Stereo-PIV and Vortex Modeling Where ? 32 Wind Y X Z

33. The VAWT in Skew: Stereo-PIV and Vortex Modeling 33 -60 mm rotational directions X Y 0°0° 90° 180° measuring planes wind -180 mm -120 mm 120 mm 180 mm 60 mm upwinddownwind Where ?

34. The VAWT in Skew: Stereo-PIV and Vortex Modeling 34 How ? Stereo PIV Method: indirect monitoring due to tracer particles the displacement is pictured via two images, taken within Δt Stereo -> 2 cameras (rotated) to quantify the out of plain motions Z X Y x y z Laser

35. The VAWT in Skew: Stereo-PIV and Vortex Modeling How ? Data Reduction 35 Evaluation Process Images

36. The VAWT in Skew: Stereo-PIV and Vortex Modeling 36 How ?Evaluation Methode : longest vorticty level Integration over the enclosed area Evaluation Process Images