Abstract
The purpose of this study is improve the predictive capability of the Dynamic Wake Meandering (DWM) model generalized to non-neutral atmospheric boundary layer (ABL) conditions in general and under stable ABL stratification in particular. The emphasis is on rotating wind turbine components, and the model improvement in focus is intimately linked to a newly developed refinement of the classic Monin-Obukhov theory, which, for stable ABL stratification, primary results in less pronounced mean wind shear outside the surface layer, where most modern wind turbines are operating. The model improvements are validated against a huge set of full-scale data, which allows for a one-to-one comparison of wind turbine load simulations and measurements conditioned on ABL stability conditions.
Highlights
For wind farm (WF) production estimation, stationary WF flow field modeling as provided by e.g. full CFD RANS models or fast linearized CFD RANS models [1] may suffice
This is explained by the difference in turbulence intensity associated with the investigated atmospheric boundary layer (ABL) stability conditions, where unstable conditions causes a turbulence level of 9.8%, neutral conditions corresponds to a turbulence level of 6.0%, and stable conditions corresponds to a turbulence level of 1.99%
In the inflow sector 150deg. –180deg. the investigated WT is not affected by upstream wakes, and it is possible to evaluate the impact from ABL stability on solitary WT loading
Summary
For wind farm (WF) production estimation, stationary WF flow field modeling as provided by e.g. full CFD RANS models or fast linearized CFD RANS models [1] may suffice. For load estimation of wind turbines (WT’s) exposed to wake affected inflow conditions, a non-stationary WF flow field description is inevitable. CFD LES models must – like the DWM model – be linked to an aeroelastic model of each and every WT in a WF to provide a complete picture of the load conditions inside a WF for all design load cases This is extremely CPU demanding and considered unrealistic for design purposes even with the capacity of nowadays very powerful state-of-the-art super computer clusters. This challenge is further enhanced when including ABL stability as an additional design load case dimension and/or considering optimization of WF layout
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