Abstract: Offshore wind development is being considered along the US East Coast, where hurricanes commonly occur. Even the most stringent wind turbine designs (IEC Class I) are not yet rated to withstand winds greater than a weak Category 3 hurricane. Characteristics of the hurricane boundary layer (HBL) that can influence turbine loads, especially in major hurricanes (≥ Category 3 on the Saffir-Simpson hurricane wind scale), are poorly understood due to a lack of observations.
We use a LES model, Cloud Model Version 1 (CM1), to simulate the wind characteristics for a theoretical offshore turbine during an idealized Category 5 hurricane, the strongest class of hurricanes and thus the "worst case" scenario for wind turbine designers. The model can simulate hurricane-like wind profiles at high spatial (< 10 m) and temporal resolution (< 0.1 s).
By comparison to the limited available observations, we find that a relatively "simple" and inexpensive configuration of the CM1 model accurately represents hurricane behavior in terms of mean wind speeds, wind speed variances, and power spectra. Comparisons of HBL power spectra to the Kaimal and von Kármán spectra suggest that modifications are needed to represent the HBL. Results also indicate that flow in the HBL remains highly coherent (≥ 0.6) for much larger separations (≥ 15 m) than is seen onshore and in a non-HBL atmosphere. Coherence of turbulent structures with characteristic sizes similar to typical blade lengths (∼ 63 m) are prevalent in the HBL which might increase loads on mechanical turbine components.
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