RECOMMENDED PRACTICES WHEN ANALYZING WIND FLOW NEAR A FOREST EDGE WITH WAsP Benoit Dalp and Christia - PowerPoint PPT Presentation

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RECOMMENDED PRACTICES WHEN ANALYZING WIND FLOW NEAR A FOREST EDGE WITH WAsP Benoit Dalp and Christia

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Title: RECOMMENDED PRACTICES WHEN ANALYZING WIND FLOW NEAR A FOREST EDGE WITH WAsP Benoit Dalp and Christia


1
RECOMMENDED PRACTICES WHEN ANALYZING WIND FLOW
NEAR A FOREST EDGE WITH WAsPBenoit Dalpé and
Christian Masson
Canada Research Chair on Nordic Environment
Aerodynamics of Wind Turbines. École de
Technologie Supérieure (ÉTS), Montréal, Canada
2
Presentation overview
  • Objectives
  • Experimental measurements
  • Wind flow entering the forest
  • Wind flow leaving the forest.
  • CFD simulations
  • Mathematical model
  • Numerical method.
  • WAsP
  • Results
  • Conclusion and recommendations.

3
1. Objectives
  • Evaluate the influence of the meteorological
    station (met. station) position on the predicted
    wind flow obtained with WAsP
  • Compare WAsP to experimental measurements at low
    altitude and CFD simulations at high altitude for
    two wind flow directions.

4
2. Experimental measurements i) Wind flow
entering the forest
  • Measurements obtained by Irvine et al., 1990
  • Forest
  • Uniform Sitka Spruce plantation
  • Average height (h) 7.5m
  • LAI2.15
  • Assumed a distribution

5
2. Experimental measurements i) Wind flow
entering the forest
  • Wind velocity measurements obtained at three
    heights (z/h 0.5, 1, 2) on four masts

6
2. Experimental measurements ii) Wind flow
leaving the forest
  • Measurements obtained by Raynor, 1971
  • Forest
  • Pine forest
  • Average height (h) 10.5m
  • Assumed a distribution

7
2. Experimental measurements ii) Wind flow
leaving the forest
  • Wind velocity measurements obtained at four
    heights (z/h 0.17, 0.33, 0.67, 1.33) on five
    masts

8
3. CFD simulations i) Mathematical model
  • Two dimensionnal (x-z)
  • Incompressible flow
  • Steady state
  • Neutral stratification
  • Negligible Coriolis force
  • Horizontally homogeneous forest.

9
3. CFD simulations i) Mathematical model
  • Momentum source term
  • Cd forest drag coefficient
  • a leaf area density.

10
3. CFD simulations i) Mathematical model
  • k-e turbulence model
  • Original constants Jones and Launder,
    1972
  • Modified constants Katul et al., 2004

11
3. CFD simulations i) Mathematical model
  • Source terms in k and e equationsKatul et al.,
    2004

12
3. CFD simulations ii) Numerical method
  • Numerical solution with FLUENT 6.2
  • Mesh with Gambit 2.2 for two directions
  • Wind flow enteringthe forest
  • Wind flow leavingthe forest

13
3. CFD simulations ii) Numerical method (wind
flow entering the forest)
  • Boundary conditions
  • Inlet and top of the domain

14
3. CFD simulations ii) Numerical method (wind
flow entering the forest)
  • Outlet boundary Patankar, 1980 outflow
    condition
  • On the ground outside the forest shear
    boundary condition of Richards and Hoxey,
    1993
  • On the ground inside the forest transition
    from a shear boundary condition to a full slip
    wall.

15
3. CFD simulations ii) Numerical method (wind
flow leaving the forest)
  • Boundary conditions
  • Same as for wind flow entering the forest except
    for the inlet and top boundary
  • At the inlet and top boundary a fully
    developed solution was used.

16
3. CFD simulations ii) Numerical method (wind
flow leaving the forest)
  • Fully developed solution with FLUENT 6.2
  • Boundary conditions
  • Ground full slip wall
  • Top constant friction velocity.

17
4. WAsP
  • Forest representationDellwick et al.,
    2004d displacement height 0.65
    hzo roughness length 0.1 hWAsP users
    guide

18
4. WAsP
  • Zero heat flux was imposed to simulate a neutral
    atmosphere
  • For each wind flow direction (entering and
    leaving the forest), nine met. station positions
    were considered.

19
5. Resultsi) Wind flow entering the forest
  • Meteorological station positions

20
5. Results i) Wind flow entering the forest
21
5. Resultsii) Wind flow leaving the forest
  • Meteorological station positions

22
5. Results ii) Wind flow leaving the forest
23
6. Conclusion and recommendations
  • For each wind flow direction, nine different met.
    station positions in WAsP were considered
  • Predictions obtained from WAsP were compared to
    experimental measurements at low altitude and to
    CFD simulations at high altitude

24
6. Conclusion and recommendations
  • When in the neighbouring of a forest edge, WAsP
    is very sensitive to the met. station position
  • Compared to CFD simulations, WAsP had differences
    up to 20 at typical hub height
  • To obtain acceptable results, the met. station
    should be located outside the forest or above the
    forest at z gt 5h.

25
Acknowledgments
  • NSERC for the funding of this research
  • CORUS Center in Murdochville, Canada, for the
    WAsP license.
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