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Micro- and meso -scale effects of forested terrain

Micro- and meso -scale effects of forested terrain. Ebba Dellwik, Jakob Mann, Andrey Sogachev, Joakim Refslund Nielsen and Andrea Hahmann. What characterizes the wind climate over a very large forest ?. Sites. How much does it matter, where a large forest is located ?.

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Micro- and meso -scale effects of forested terrain

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  1. Micro- and meso-scale effects of forested terrain Ebba Dellwik, Jakob Mann, Andrey Sogachev, Joakim Refslund Nielsen and Andrea Hahmann

  2. Whatcharacterizes the windclimate over a very large forest? Sites Howmuchdoes it matter, where a large forest is located? Howcanweminimize the effect of treeson the turbine windclimate?

  3. S1: 100m tall mast Sonicanemometers at 33 and 97mForestheight 25m (2000)

  4. S1 turbulenceintensity x x x Title of the presentation

  5. x x x S1 shear

  6. Turbulent structures in forested areas Gust structure and generation in canopy flows, Segalini et al., PO 457

  7. Sitingchallenge: large forestedarealike S1 • The turbine shouldbetall to avoidextremeshear, highturbulence and turbulent events near the surface. • What is the windresource in the range 100-250m? Effects of ”weather” and land surfaceon flow. The meso-scale flow models predict the dailycycle of temperature, wind, humidity up to about 15km. The height of the boundarylayer and surfaceenergy balance areimportant. Forest is representedwith a roughness, typicallylessthan 1m Resolution ~ 1km

  8. Sitingchallenge: small forests Howcanweminimize the effect of treeson the turbine windclimate? Weperformexperimentswith the aim of verifying and improvingourmicro-scale models. Micro-scalefocus: the effect of terrainon flow, for example a forestedge, a hillor an escarpment. The micro-scale flow models primarilypredict the flow whenthere is notemperature gradient. Resolution ~ 1-10m The forest is represented as a distributed drag force.

  9. S2: Two 45m masts1 horizontallypointinglidarForestheight 24m

  10. LIDAR and CFD modellingresults U

  11. Micro-scale model applications Optimizedsiting of turbines

  12. Howmuchdoes it matter, where a large forest is located? S3: Mast 38mLidarprotoype at 28mForestheight 24-28m

  13. Satellite image of September 14th 00:00 Title of the presentation

  14. September 13th-14th, 2010 Preliminaryresults

  15. S3: hypothesis Warm air from the sea is advected in over the relativelycolderSwedishwest coast. Thiscreates a stablystratified atmospherewhichsuppresses the forest turbulence.

  16. Summary • Whatcharacterizes the windclimate over a very large forest? S1: highshear and turbulenceintensityexceeding the IEC standard, regular events of fast changingwind speed. -> Possibility to make turbines talleror more robust. • Howcanweminimize the effect of treeson the turbine windclimate? S2: improvement of micro-scale models by detailednear-forestexperiment. -> Improve and run reliablemicro-scale models to optimize the siting of turbines. • Does it matter where the large forest is located? S3: yes! Preliminaryresults point to effects from areas >100km upstream of the site. More measurementsareneeded. -> Improve and run meso-scale models!

  17. Acknowledgements • Meelis Mölder and Anders Lindroth at Lund University for use of data from site S1. • Leif Klemedtsson at GothenburgUniversity for access to the mast at the S3 site. Thankyou for your attention!

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