Study on Wind Farm Flow Field Characteristics Based on Boundary Condition Optimization of Complex Mountain Numerical Simulation
Abstract
:1. Introduction
2. Methodology
3. Case Analysis of Wind Farms in Complex Terrains
3.1. Introduction to the Wind Farm
3.2. On-Site Measurement and Wind Data Processing
3.3. Numerical Simulation
3.3.1. Geometric Model and Computational Domain
3.3.2. Mesh Division and Mesh Independence
3.3.3. Boundary Conditions and Operating Conditions
3.3.4. CFD Simulation Results Validation
4. Results and Discussion
4.1. Flow Field Characteristics under Different Wind Directions
4.1.1. Mean Wind Speed
4.1.2. Turbulence Intensity
4.2. Local Terrain Impact under the Same Wind Direction
4.2.1. Changes in Local Streamlines
4.2.2. Local Turbulence Intensity
5. Conclusions
- Terrain Modeling: Considering the impact of “man-made cliffs”, a transitional curve that restores the original terrain variations within the transition section is used. To avoid grid errors, a cylindrical fluid domain is established, and the range of the inlet and outlet areas is flexibly selected to achieve wind direction conversion. In terms of boundary conditions, the inlet wind speed is corrected by the acceleration ratio to obtain a flow field distribution that is closer to reality.
- Wind Measurement Data Analysis: The analysis of the wind measurement tower data shows a dominant wind direction concentrated in the W sector, accounting for 23.59% of occurrences, followed by the WSW and SSE sectors, with frequencies of 19.05% and 12.77%, respectively. Most wind speeds vary between 5 m/s and 10 m/s. Turbulence intensity mainly ranges from 0.1 to 0.3, generally indicating low to moderate turbulence intensity.
- Applicability of the New Method: The proposed method shows good applicability to complex terrain wind farms. Comparing numerical simulations with field-measured wind speed and direction, the wind speed error is within 6%, and the wind direction error is within 15°, indicating a certain degree of accuracy. Combining numerical simulations with measured data can recreate the actual flow field near the wind measurement tower, providing practical guidance for engineering.
- Flow Field Characteristics Comparison: Comparing the flow field characteristics under different wind directions reveals a significant terrain shielding effect on both wind speed distribution and turbulence intensity. The wind speed distribution and turbulence intensity are particularly evident under 120° and 150° wind directions, due to a ridge line in the terrain that is almost perpendicular to the incoming wind. When the incoming wind reaches the ridge or hilltop, it forms a low-speed wake region behind, where the wind speed decreases, the turbulence intensity increases, and the flow field becomes unstable.
- Terrain Impact on Flow Field: To observe the terrain impact under the same wind direction, a ridge section almost perpendicular to the incoming wind and unaffected by other terrain features is selected. Changes in the lateral wind profile and turbulence intensity at the measurement points are observed. The results show that the flow field in complex terrains is significantly affected by terrain variations and the cumulative impact of continuous terrain changes, leading to inconsistent patterns. Overall, high-acceleration flow field regions are less affected by turbulence and eventually achieve higher wind speeds.
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
Nomenclature and Abbreviations
Adjusted terrain elevation (m) | |
Original terrain coordinate point elevation (m) | |
Radius of the actual terrain to be preserved (m) | |
Length of the transition section (m) | |
Average wind speed at a certain height z at the meteorological mast (m/s) | |
Wind speed 10 m above the ground obtained from the analysis of wind measurement data (m/s) | |
Ground roughness | |
Height (m) | |
Average wind speed at a certain height above the ground in the wind measurement data (m/s) | |
Average wind speed at the same height as in the first numerical simulation (m/s) | |
Wind acceleration ratio | |
The inlet velocity of the second numerical simulation (m/s) | |
Numerical simulation of turbulence intensity | |
Wind speed value at height z in the numerical simulation (m/s) | |
Turbulence kinetic energy (m2/s2) | |
Physical height of the roughness | |
Roughness constant | |
Roughness length | |
Turbulence intensity at height z | |
Turbulence dissipation rate (m2/s3) | |
Coefficient for the turbulent viscosity | |
Turbulence integral scale | |
Gradient height (m) | |
Tower wind speed of numerical simulation (m/s) | |
Tower wind speed of wind measurement tower (m/s) | |
Wind directions of wind numerical simulation (°) | |
Wind directions of wind measurement tower (°) | |
CFD | Computational fluid dynamics |
RANS | Reynolds-averaged Navier–Stokes |
LES | Large eddy simulation |
NWP | Numerical weather prediction |
BTS | Boundary transition slope |
BOI | Body of Influence |
UDF | User defined function |
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Wind Field Type | Description | Ground Roughness Index α | (m) |
---|---|---|---|
A | Offshore sea and islands, coasts, lakeshore, and desert areas | 0.12 | 300 |
B | Fields, villages, jungles, hills, and towns with sparse houses | 0.15 | 350 |
C | An urban area with a dense cluster of buildings | 0.22 | 450 |
D | An urban area consisting of a dense group of buildings with taller buildings | 0.30 | 550 |
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Wang, X.; Hu, J.; Deng, K.; Zhang, M.; Shen, S.; Shen, Y.; Chen, S.; Pan, W.; Wen, R.; Kang, W.; et al. Study on Wind Farm Flow Field Characteristics Based on Boundary Condition Optimization of Complex Mountain Numerical Simulation. Processes 2024, 12, 1885. https://doi.org/10.3390/pr12091885
Wang X, Hu J, Deng K, Zhang M, Shen S, Shen Y, Chen S, Pan W, Wen R, Kang W, et al. Study on Wind Farm Flow Field Characteristics Based on Boundary Condition Optimization of Complex Mountain Numerical Simulation. Processes. 2024; 12(9):1885. https://doi.org/10.3390/pr12091885
Chicago/Turabian StyleWang, Xiuru, Jianliang Hu, Kai Deng, Mingjie Zhang, Shizhao Shen, Yunshan Shen, Sheng Chen, Weijie Pan, Ruifeng Wen, Weiwei Kang, and et al. 2024. "Study on Wind Farm Flow Field Characteristics Based on Boundary Condition Optimization of Complex Mountain Numerical Simulation" Processes 12, no. 9: 1885. https://doi.org/10.3390/pr12091885