UH
U. Hussain
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Aeroelastic Response of a 22 MW Offshore Wind Turbine Under Varying Atmospheric Stability
An Investigation of Torsional Blade Flexibility and ABL Stability Effects on Aerodynamic and Structural Loading
The continued upscaling of offshore wind turbines toward the 20 MW class introduces significant aeroelastic and atmospheric challenges not fully captured by conventional structural models and simplified inflow assumptions. As rotor blades grow increasingly long and slender, torsional flexibility and bend-twist coupling become non-negligible factors in determining the aerodynamic and structural response of the rotor. This thesis investigates the influence of torsional degrees of freedom and atmospheric boundary layer stability on the aerodynamic performance and structural loading of the IEA 22 MW reference wind turbine, using OpenFAST with LES-generated turbulent inflow across below-rated, rated, and above-rated operating conditions. ElastoDyn overestimates rotor thrust by 7.0% at below-rated conditions compared to BeamDyn, driven by its rigid torsion assumption neglecting nose-down blade twist. The atmospheric stability analysis reveals that stable stratification produces the highest flapwise damage equivalent load at rated conditions despite having the lowest load variability, while unstable conditions produce approximately 10% higher torsional fatigue loading at above-rated conditions. These findings demonstrate that both structural modeling fidelity and atmospheric stability class have significant consequences for load and fatigue assessment of large offshore wind turbines.
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The continued upscaling of offshore wind turbines toward the 20 MW class introduces significant aeroelastic and atmospheric challenges not fully captured by conventional structural models and simplified inflow assumptions. As rotor blades grow increasingly long and slender, torsional flexibility and bend-twist coupling become non-negligible factors in determining the aerodynamic and structural response of the rotor. This thesis investigates the influence of torsional degrees of freedom and atmospheric boundary layer stability on the aerodynamic performance and structural loading of the IEA 22 MW reference wind turbine, using OpenFAST with LES-generated turbulent inflow across below-rated, rated, and above-rated operating conditions. ElastoDyn overestimates rotor thrust by 7.0% at below-rated conditions compared to BeamDyn, driven by its rigid torsion assumption neglecting nose-down blade twist. The atmospheric stability analysis reveals that stable stratification produces the highest flapwise damage equivalent load at rated conditions despite having the lowest load variability, while unstable conditions produce approximately 10% higher torsional fatigue loading at above-rated conditions. These findings demonstrate that both structural modeling fidelity and atmospheric stability class have significant consequences for load and fatigue assessment of large offshore wind turbines.