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New developments on thermal stability
in Meteodyn WT
K. Fahssis, C.Bezault, D.Delaunay
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Stability effects modeling in Meteodyn WT
Validation studies
Integrating stability effects in the AEP estimation
Contents
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Challenges for introducing thermal stability in a long term statistical assessment:
Great number of meso-scale configurations Transient nature of thermal stability (diurnal cycle) Correlation with wind speed and direction Integration of the thermal stability effects at micro-scale
Two approaches for the numerical methods
1/ NS equations + Heat transport equation
Combining transient meso and micro scale computations Ground model (albedo, ground temperature, conductivity, soil humidity) Radiative fluxes (solar, infra-red) Selection of a limited number of « homogeneous events »
2/ NS equations + Turbulent length scale profiles
Steady NS equations solved for given direction and stability class Statistical analysis of the triplet (wind direction and speed, stability class) A stability class defines a turbulent length scale profile and inlet boundary conditions
Thermal stability and AEP assessment
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Reynolds Averaged Navier Stokes equations - Stationary flow
Closure of the system (turbulence modeling):
Equations
0
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x
u
0''
ijii
j
j
i
jij
ij Fuux
u
x
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P
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itji x
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uuu ''
TT Lk 2/1where
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j
j
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iTk
T
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jk
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x
U
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UP
kL
C
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2
Equations
Transport equation for the turbulent kinetic energy
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lSL mT232
Evaluation of the turbulent length scale:
- Consideration of the thermal stratification
- Models of Yamada (1983) and Arritt (1987)
085.0:16.0
)2231.0)(1(
)2341.0)(1912.0(96.1:16.0
mif
ifif
ififmif
SR
RR
RRSR
zll /1/1/1 0
ifR Flux Richardson number
Equations
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Log – linear law profiles on homogeneous terrain
Validations
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2D hill: Experiment of Ross et al. (2004)Boundary-Layer Meteorol. 113, 427-459
Experiment: neutral Experiment: stable
h = Hcos²(p x/L)H = 229 m (full-scale) L = 1000 mz0 = 1 m (canopy model)
WT neutral
WT stable: LMO=400 m
Validations
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Integrating the thermal stratification
in AEP assessment
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Meteorological Data
Time series Speed/direction joint frequencies Speed/direction/stability joint frequencies
Thermal stability and AEP assessment
Wind speed coefficientsTurbulence intensityWind shearWind direction
Orography map
Roughness map
Met masts and wind turbines locations
Wind flow computation: one direction sector one stability class
AEP , IEC export
Integration Process
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On site Turbulence measurements
(LIDAR, SODAR, met mast)
Standard deviation of:Vertical wind speedHorizontal wind speedHorizontal wind directionHeat and momentum vertical fluxes
Stability Classes
On site Gradient measurements
(met mast, LIDAR, SODAR)
10-min mean values of:Mean wind speedMean air temperature
Richardson Number Obukhov Length
Stability Classes
Regional data(weather station, meso-scale data)
Mean Wind speedSolar radiation (daily)Snow (daily)Hour, season
Stability Classes
Time series of wind speed, direction, stability class Tables of joint frequency tables speed/direction/stability
Thermal stability and AEP assessment
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AEP assessment of a wind farmin the North-East of France
Speed Coefficients for 3 stability classes
Wind direction: 60 deg
unstable : LMO = - 80 m neutral stable : LMO = 500 m
Thermal stability and AEP assessment
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Wind Direction 60 degRoughness length = 6 cm – 65 cm
Wind profiles at the met mast(Maïa Eolis measurements)
Thermal stability and AEP assessment
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Stability Class LMO (m) Mean hourly
production (kWh)
Frequency Contribution(MWh/an)
Unstable - 80 4900 0.07 2575
Slightly unstable - 500 5250 0.18 8278
Neutral 10000 5480 0.45 21602
Slightly stable 1500 4300 0.12 4520
Stable 800 2600 0.11 2505
Very stable 300 1530 0.07 938
TOTAL - - 1.00 41040
Thermal stability and AEP assessment
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Stability effects: Works in progress
- Analysis of Hovsore and Horns Rev profiles (A.Peña, 2009)- New sites by Maïa Eolis (multiple 80 m masts)- Calibrating LMO inside WT code as a function of « experimental » LMO
- Most relevant parameters from a statistical point of view- Application to the Meteodyn forecast module
Acknowledgements
French Environment and Energy Management Agency Research funding
French Ministry for Research Research funding
Maïa Eolis On site measurements and scientific partnership
Conclusion
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THANK YOU FOR YOUR ATTENTION!