Structural Response of 34‐m Darrieus Rotor to Turbulent Winds

The results of a mathematical investigation of the dynamic response of the Sandia/Department of Energy/U.S. Department of Agriculture 34‐m‐diameter Darrieus rotor wind turbine erected at Bushland, Tex., are presented. The formulation used a double multiple stream‐tube aerodynamic model combined with a turbulent airflow and included the effects of (linear) aeroelastic forces. The structural analysis was carried out using previously established procedures with the computer program MSC/NASTRAN. A number of alternative expressions for the spectrum of turbulent wind were used. The modal loading represented by each did not differ significantly; a more significant difference was caused by imposing full lateral coherence of the turbulent flow. Spectra of the predicted stresses at various locations show that without aeroelastic forces, very severe resonance is likely to occur at certain natural frequencies. Inclusion of aeroelastic effects greatly attenuates this stochastic response, especially in modes involving in‐plane blade bending. Comparison is made with preliminary field data collected at medium‐low wind speeds (11.3 m/s) from critical locations on the blade. This comparison shows generally good agreement between measured stress spectra and model predictions based on 10% turbulence intensity and including aeroelastic forces.