1. Wind Resource Reconstruction In Complex Terrains Regarding Thermal Stratification
Chengcheng Chen, Tingting Jiang, Genyong Wu
State Key Laboratory of Wind Power System, China
Zhejiang Windey Co., Ltd, China
Chi-Yao Chang, Xiao Wang, Bernhard Stoevesandt
Fraunhofer IWES, Germany

2. Introduction
Methodology
Results analysis
Summary

3. Objectives
Development of a methodology to calculate the wind resource in complex terrain wind farm, cooperating with Fraunhofer IWES:
Topography capture by an advanced mesh strategy, key feature, less element…
Derive distinct thermal stratification classes from Met. Mast data, and execute the CFD simulation with the extended simpleFoam.
Obtain the wind data of the target position by a speed up ratio matrix of wind sectors and atmospheric stability.

4. Monin-Obukhov Similarity theory
Mean velocity profile in homogeneous flat plane with heat transfer correct the log-law to
(stable stratification)
(neutral)
(unstable stratification)
Vertical heat flux induced buoyant force → changing the mean velocity profile
Night time: air warmer then the ground → downward heat flux : stable condition
Day time: ground warmer than the air → upward heat flux :unstable/ convective condition

5. Buoyant induced effects on inhomogeneous boundary layer
Attached flow in stable stratified pattern
Enlarged recirculation bubble in convective state
Stable
Neutral
Unstable

6. Met mast data classification
The u*-MoL diagram provides the wind analysts an overview of the stratification conditions on the site, for which the met mast data over several height levels are fit according to Monin-Obukhov similarity law.

7. Wind farm in complex terrain
Hill land wind farm in the south east of China.
Domain size 10km×10km×2.5km
TerrainBlockMesher generated structural mesh, element 11×106
Inhomogeneous roughness distribution

8. + Processing Stable/unstable/ neutral conditions
Each simulation with 1-D precursor boundary generation
Extended k-Epsilon model for buoyant force with correction +

9. Speed-up-correlation in Stratified ABL
The general description of speed-up ratio behavior regarding two velocities based on one certain point reads:.
𝑈(𝑀𝑂𝐿,𝐷ir) 𝑎𝑖𝑚 = 𝐴(𝑀𝑂𝐿,𝐷ir) 𝑎𝑖𝑚 ∙ 𝑈(𝑀𝑂𝐿,𝐷ir) 𝑟𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒
Mol
Dir
unstable
（Mol=-1000）
（Mol=-500）
（Mol=-100）
neutral
（Mol=+∞&-∞）
stable
（Mol=500）
A(-1000, 0)
A(-500, 0)
A(-100, 0)
A(0, 0)
A(500, 0) 15
A(-1000, 15)
A(-500, 15)
A(-100, 15)
A(0, 15)
A(500, 15 ) 30
A(-1000, 30)
A(-500, 30)
A(-100, 30)
A(0, 30)
A(500, 30) 60
A(-1000, 60)
A(-500, 60)
A(-100, 60)
A(0, 60)
A(500, 60) 90
A(-1000, 90)
A(-500, 90)
A(-100, 90)
A(0, 90)
A(500, 90)
120
A(-1000, 120)
A(-500, 120)
A(-100, 120)
A(0, 120)
A(500, 120)
150
A(-1000, 150)
A(-500, 150)
A(-100, 150)
A(0, 150)
A(500, 150)
165
A(-1000, 165)
A(-500, 165)
A(-100, 165)
A(0, 165)
A(500, 165)
180
A(-1000, 180)
A(-500, 180)
A(-100, 180)
A(0, 180)
A(500, 180)
195
A(-1000, 195)
A(-500, 195)
A(-100, 195)
A(0, 195)
A(500, 195)
210
A(-1000, 210)
A(-500, 210)
A(-100, 210)
A(0, 210)
A(500, 210)
240
A(-1000, 240)
A(-500, 240)
A(-100, 240)
A(0, 240)
A(500, 240)
270
A(-1000, 270)
A(-500, 270)
A(-100, 270)
A(0, 270)
A(500, 270)
300
A(-1000, 300)
A(-500, 300)
A(-100, 300)
A(0, 300)
A(500, 200)
330
A(-1000, 330)
A(-500, 330)
A(-100, 330)
A(0, 330)
A(500, 330)
345
A(-1000, 345)
A(-500, 345)
A(-100, 345)
A(0, 345)
A(500, 345)

10. Commercial software

11. Flow pattern regarding thermal stratification
Interaction with complex topology, stable and neutral show similar attached flow pattern.
Flow runaway upward more serious in the downstream of hill in unstable condition, because of the convective in vertical direction.
U/m·s-1
Stable
Neutral
Unstable
(Area 1)
(Area 2)
(Area 3)

12. Summary
Monin-Obukhov similarity law was used to class the thermal stratification of wind farm.
Flow over terrain could have significant different patterns due to thermal stratification class.
Taking thermal stratification into account of wind resource reconstruction in complex terrain shows the closer result.

13. Thanks for your attention!
STATE KEY LABORATORY OF WIND POWER SYSTEM
ZHEJIANG WINDEY CO.,LTD
Chengcheng Chen
CONTACT:
Thanks for your attention!