EWEA Annual Event 2013 Vienna February, 4-7, 2013

1. EWEA Annual Event 2013 • Vienna • February, 4-7, 2013 Analysis of Vortex-induced Vibrations using a free-wake aeroelastic toolSpyros Voutsinas (*)FangmaoZou(**), Vasilis Riziotis(*), Jun Wang(***)(*) NTUA, School of Mechanical Engineering, Greece(**) China-EU Institute for Clean and Renewable Energy, Wuhan, China(***) Huazhong University of Science and Technology, Wuhan, China

2. Vortex-induced vibrations & wind turbines Aeroelastic instabilities and vortex-induced vibrations can appear on wind turbine blades at stand still. • Negative (CL-a) slope a~90o triggers Aeroelastic instabilities • Large vortex structures trigger Vortex induced vibrations Du96-w-180: Skrzypiński et al, DTU 2012

3. Validation Good agreement in the prediction of the lift slope, critical for aeroelastic damping characterization The double wake model Cdmax Clmax Clmin Cdmax v-, P+ v+, P- v+, P- v-, P+ Finite:

4. Validation PSD of CL PSD of CD about 10% shift in vortex shedding frequency PSD of CL PSD of CD

5. Forced vibration results max appears at vibration periods 9.7 or 9.8 which are close to the vortex shedding period 10. -curve of different A*/T* Cl time series with different A*/T*, α=90

6. Forced vibration results (a) (b) (c) (d) T*=10 (e) T*=11 (f) T*=13 Cl-x plot of A*/T*=0.03 series

7. Typical blade section model u w Aeroelastic simulations V u: edgewise displacement w: flapwise displacement 𝜃: torsional angle k: spring coefficient : the distance between the gravity center and the elastic axis V: inflow velocity Structural model with 3 d.o.f.

8. eigenvalue stability analysis m=165 kg/m, fflap=0.7 hz, fedge=1.1 hz c=2.8 m (r/R=0.7), d=1.25% (=0.2%) high damping of flap mode driven by high CD value flap mode edge mode damping of edge mode driven by negative slope of CL and CD value wind speed 25 m/s damping driving parameter Aeroelastic simulations

9. eigenvalue stability analysis: reference to “reality” 3D aerodynamic characteristics m=165 kg/m, fflap=0.7 hz, fedge=1.1 hz c=2.8 m (r/R=0.7), d=1.25% (=0.2%) edge mode wind speed 25 m/s damping driving parameter Aeroelastic simulations

10. eigenvalue stability analysis – effect of mass and chord length wind speed 25 m/s Aeroelastic simulations C=2.8 C=1.6

11. eigenvalue stability analysis – effect of structural properties m=165 kg/m, c=2.8 m: (Rf=0.021) wind speed 25 m/s fflap=0.7 hz, fedge=1.1 hz Aeroelastic simulations Edge frequency structural pitch

12. non-linear aeroelastic stability analysis m=165 kg/m, c=2.8 m (Rf=0.021) wind speed 25 m/s fflap=0.7 hz, fedge=1.1 hz 10s excitation period at the frequency of the edge mode (1.1 hz) Strongly non linear behaviour. Difficult to measure damping aoa = 90o Aeroelastic simulations

13. non-linear aeroelastic stability analysis m=165 kg/m, c=2.8 m (Rf=0.021) wind speed 25 m/s fflap=0.7 hz, fedge=1.1 hz aoa = 100o Aeroelastic simulations

14. analysis of lock-in due to vortex shedding m=165 kg/m, c=2.8 m (Rf=0.021) fflap=0.7 hz, fedge=1.1 hz U=10 m/s U=15 m/s U=20 m/s fs1=0.36hz fs2=0.71hz fs1=0.54hz fs2=1.07hz fs1=0.71hz fs2=1.43hz Aeroelastic simulations

15. analysis of lock-in due to vortex shedding m=165 kg/m, c=2.8 m (Rf=0.021) fflap=0.7 hz, fedge=1.1 hz U=25 m/s U=30 m/s U=35 m/s fs1=0.89hz fs2=1.79hz fs1=1.07hz fs2=2.14hz fs1=1.25hz fs2=2.50hz Aeroelastic simulations

16. Conclusions • The double wake model has been successfully applied • The cut-off length acts as calibration parameter. Good results were obtained for relatively large values • Lock-in was detected at the shedding frequency corresponding to T~10. • The positive feedback between the lock-in phenomenon and the structural vibration is found to be the main reason for the vortex induced aero-elastic instability.

17. Thanks for your attention END

18. analysis of lock-in due to vortex shedding m=165 kg/m, c=2.8 m (Rf=0.021) fflap=0.7 hz, fedge=1.1 hz flapwise deflection flap deflection edgewise deflection Aeroelastic simulations