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Floating Offshore Wind Turbine Aerodynamics and Optimization Opportunities

Floating Offshore Wind Turbine Aerodynamics and Optimization Opportunities. Evan Gaertner University of Massachusetts, Amherst egaertne@umass.edu IGERT Seminar Series October 1st, 2015. Agenda. Floating Wind Turbine Aerodynamics Dynamics Stall Design Optimization.

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Floating Offshore Wind Turbine Aerodynamics and Optimization Opportunities

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  1. Floating Offshore Wind Turbine Aerodynamics and Optimization Opportunities Evan Gaertner University of Massachusetts, Amherst egaertne@umass.edu IGERT Seminar Series October 1st, 2015

  2. Agenda • Floating Wind Turbine Aerodynamics • Dynamics Stall • Design Optimization

  3. Floating Offshore Wind Turbines Advantages: • Access to deeper water • More useable area • Further from onshore lines of site • Reduce impact to important near shore habitats • Simplified installation • Tow-out installation • Reduce environmental impacts from pile driving

  4. Platform Motion • Wind and wave loading • Non-rigid mooring system • Complex platform motion • 6 transitional and rotational Degrees of Freedom • Adverse Affects: • Increased aerodynamic complexity • Stronger cyclical loading • Requires more sophisticated controls

  5. Velocity from Platform Motion Wake interaction • From pitch or surge • Rotor moves through its own wake • Can causes flow reversals and turbulence • Occurs at platform motion frequency Skewed flow • From pitch or yaw • Blade moves • Toward wind: increased velocity • Away from wind: decreased velocity • Occurs at rotational frequency

  6. Wake Induced Dynamic Simulator (WInDS) • A free-vortex wake method • Developed to model rotor-scale unsteady aerodynamics • By superposition, local velocities are calculated from different modes of forcing • Previously neglected blade section level, unsteady viscous effects [2]

  7. Blade Scale Unsteadiness

  8. Quasi-Steady Aerodynamics • Aerodynamic properties of airfoils determined experimentally in wind tunnels • Lift increases linearly with angle of attack (α) • At a critical angle, flow separates and lift drops • “Stall” • WInDS used quasi-steady data

  9. Dynamic Stall

  10. Dynamic Stall Flow Morphology Lift Coef, CL Drag Coef, CD Moment Coef, CM Angle of Attack, α (°) Angle of Attack, α (°) Angle of Attack, α (°) [3]

  11. Modeling Dynamic Stall: Leishman-Beddoes (LB) Model • Semi-empirical method • Use simplified physical representations • Augmented with empirical data • Model Benefits • Commonly used, well documented • Minimal experimental coefficients • Computationally efficient [3]

  12. Example 2D LB validation: S809 Airfoil, k = 0.077, Re = 1.0×106 LB model validated against 2D pitch oscillation data

  13. WInDS-FAST Integration • WInDS was originally written as a standalone model in Matlab • Decouples structural motion and the aerodynamics • Integrated into FAST v8 by modifying the aerodynamic model, AeroDyn • Fully captures the effects of aerodynamics and hydrodynamics on platform motions  changes the resulting aerodynamics OC3/Hywind Spar Buoy

  14. Design Optimization

  15. Rotor Design Design Process • Start with known optimal blade shape • Modify for practical structural and manufacturing concerns Problem • Uses ideal conditions for aerodynamic analysis: uniform, steady, non-skewed flow Typical optimization projects in the literation: • More sophisticated models • More design variables

  16. Research Goal • Inform design process with realistic probability distributions of steady and unsteady condition • Operating conditions are never ideal! • Include minimization of load variability as a design goal

  17. Integrated Design of Offshore Wind Turbines Process: • Sequential design of subsystems Problem: • Optimized subsystems • Sub-optimal global system Solution: • Multi-objective, multi-disciplinary, iterative optimization Turbine Design Platform Design Controls

  18. Interdisciplinary Opportunities Additional design goals could include: • Lower tip speed ratios • Reduce risk of bird strikes • Larger turbine rotors • Allow smaller wind farms with fewer seafloor disturbances • Optimization for deeper waters farther from shore • Reduce competition for use or view-shed concerns Open to suggestions for other interdisciplinary objects!

  19. Thank You! Questions? Evan Gaertner egaertne@umass.edu This work was supported in part by the NSF-sponsored IGERT: Offshore Wind Energy Engineering, Environmental Science, and Policy and by the Edwin V. Sisson Doctoral Fellowship

  20. Supplemental Slides

  21. Span-wise Unsteadiness • AoA predominately varying cyclically with rotor rotation, driven by: • Mean platform pitch: ~4-5° • Rotor shaft tilt: 5°

  22. Dynamic Stall

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