Wake effects of large offshore wind farms on the mesoscale atmosphere

Publication: Research - peer-reviewPoster – Annual report year: 2012

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We present a new approach, which allows us to simulate the flow distortion caused by the thrust of wind farms in a mesoscale model. The atmospheric flow is simulated with the WRF mesoscale model, since it has significantly lower computational costs compared to higher resolution models. Due to the fact that its typical horizontal grid spacing is on the order of 2km, the energy extracted by the turbine, as well as the wake development inside the turbine-containing grid-cells, are not described explicitly, but are parametrized as another sub-grid scale process.
In order to appropriately capture the wind farm wake recovery and its direction, two properties are important, the total energy extracted by the wind farm and its velocity deficit distribution. In the
considered parametrization the individual turbines apply a thrust dependent on a local sub grid scale velocity, which is influenced by the up-stream turbines. For the sub-grid scale velocity deficit, the
entrainment from the free atmospheric flow into the wake region, is taken into account. Furthermore, since the model horizontal distance is several times larger then the turbine diameter, it has been
assumed that the generated turbulence and dissipation are balanced. From version 3.2.1 onwards, the WRF model includes a wind farm parametrization option (Fitch-Scheme). Contrary to the above described parametrization where the wind turbines are positioned explicitly, the wind farms in the default scheme are treated as a density distribution, which limits the description of the internal wind farm velocity deficit development and its related efficiency. In the Fitch-scheme the extracted force is proportional to the turbine area interfacing a grid-cell. The subgrid scale wake expansion is achieved by adding turbulence kinetic energy to the flow. The validity of both wind farm parametrizations has been verified against observational data. We use met. mast measurements and power measurements from wind turbines, at HornsRev. The wind farm measurements have been used to compare the total thrust produced by both types of parametrization, as well as the down-stream velocity recovery in the first 6km after the wind farm.
Original languageEnglish
Publication date2012
Number of pages1
StatePublished

Conference

ConferenceEWEA 2012 - European Wind Energy Conference & Exhibition
CountryDenmark
CityCopenhagen
Period16/04/1219/04/12
Internet addresshttp://events.ewea.org/annual2012/

Keywords

  • EWEA 2012
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