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Mattias Mohr, Johan Arnqvist, Hans Bergström Uppsala University (Sweden)

Simulating wind and turbulence profiles in and above a forest canopy using the MIUU mesoscale model. Mattias Mohr, Johan Arnqvist, Hans Bergström Uppsala University (Sweden). Project and Goals. Project: Wind power over forests ( Vindforsk III)

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Mattias Mohr, Johan Arnqvist, Hans Bergström Uppsala University (Sweden)

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  1. Simulating wind and turbulence profiles in and above a forest canopy using the MIUU mesoscalemodel Mattias Mohr, Johan Arnqvist, Hans Bergström Uppsala University (Sweden)

  2. Project and Goals • Project: Wind power over forests (Vindforsk III) • Better estimation of energy yield (wind resource) • Better estimation of turbine loads (wind shear, turbulence, forest clearings) • Models should be developed for these purposes

  3. MIUU mesoscale model • Used for wind resource mapping of Sweden (e.g. www.weathertech.se) • Higher order closure, prognostic TKE, no terrain smoothing, 1km resolution • Very high resolution in PBL (for canopy modelling: 1, 3, 6, 10, 16, 24, 35, 52, … m)

  4. Windprofile over forests (conceptual)

  5. How to include this in model? • Drag term for horizontalwindcomponents (u, v) LAD| horizontal | u(same for v-component) whereu = hor. wind speed, Cd = 0.2 (drag coefficient), LAD =leaf area density (Lalic and Mihailovic (2004))

  6. Howtoincludethis in the model? • Production/dissipation term in TKE equation LAD | horizontal | 3 - | horizontal | q2 where q2 = turbulent kineticenergy, βp = canopy TKE-productioncoefficient, βd = canopydissipationcoefficient  These terms seemto make littledifference.

  7. ”Elevated” MoninObukhovtheory in model • Substitute all terms with elevation abovegroundthrough elevation abovezerodisplacement • Replace MO-similaritytheory terms belowzerodisplacementheightwithsomethingelse (what?) • Lowerboundaryconditionshaveto be modified

  8. Master lengthscale • Master lengthscalewithinforest has to be modified • We chose simple modelofInoue (1963): l = 0.47 · (h – d) ≈ 2m • Lengthscaleconstantwithheightwithincanopy • However, this has verylittleinfluence on results

  9. Energy balance • Has to be solved at eachmodellevelwithincanopy • ShortwaveradiationfollowsroughlyBeer’slawS↓ = S↓0 · exp(-0.5 · ) • Longwaveradiation (Zhao and Qualls, 2006)

  10. Summary

  11. Start with idealised 1D simulations • Compare new simulatedprofileswithprofiles from bulk layermodel version and measurements • Useforest drag terms in horizontalmomentumequations and canopyenergybalance (not in TKE equation) • Run 24 hours (diurnalcycle) and takemeanvalue • Parameters used: 10m/s geostr. wind, averagetemperatureprofile, z0 = 1m, h = 20m, LAI = 5, pineforest, total cloudiness = 50%

  12. Preliminary 1D results

  13. Comparisonwithmeasurements

  14. Comparisonwithturbulencemeasurements

  15. Summary & Conclusions • Preliminary 1D resultspromising • Still a lotofworkto do (lowerboundaryconditions, canopyenergybalance, lengthscale…) • Vertical resolution of 1D resultsmight be tootime-consumingtorun in 3D • Is vertical resolution of 3D runs (2, 6, 12, 21, 33, 49, 72, 103, …m) enough for canopymodel?

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