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Explore aerodynamics and design optimization of floating offshore wind turbines for advantages like deeper water access, simplified installation, and reduced environmental impact. Learn about platform motion, dynamic stall, wake interaction, and the use of innovative simulation methods. Discover the integration of models for improved design processes and the optimization challenges faced in turbine and platform design. Explore interdisciplinary opportunities and additional design goals in this evolving field.
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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
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
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
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
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]
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
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]
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]
Example 2D LB validation: S809 Airfoil, k = 0.077, Re = 1.0×106 LB model validated against 2D pitch oscillation data
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
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
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
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
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!
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
Span-wise Unsteadiness • AoA predominately varying cyclically with rotor rotation, driven by: • Mean platform pitch: ~4-5° • Rotor shaft tilt: 5°