TY - JOUR
T1 - Interaction between low-level jets and wind farms in a stable atmospheric boundary layer
AU - Gadde, Srinidhi N.
AU - Stevens, Richard J. A. M.
N1 - Funding Information:
This work is part of the Shell-NWO/FOM-initiative Computational sciences for energy research of Shell and Chemical Sciences, Earth and Live Sciences, Physical Sciences, Stichting voor Fundamenteel Onderzoek der Materie, and Stichting voor de Technische Wetenschappen (STW). This work was carried out on the national e-infrastructure of SURFsara, a subsidiary of SURF corporation, the collaborative ICT organization for Dutch education and research, and an STW VIDI Grant (No. 14868).
Publisher Copyright:
© 2021 American Physical Society.
PY - 2021/1/14
Y1 - 2021/1/14
N2 - Low-level jets (LLJs) are the wind maxima in the lower regions of the atmosphere with a high wind energy potential. Here we use large-eddy simulations to study the effect of LLJ height on the flow dynamics in a wind farm with 10 × 4 turbines. We change the LLJ height and atmospheric thermal stratification by varying the surface cooling rate. We find that the first row power production is higher in the presence of a LLJ compared to a neutral reference case without LLJ. Besides, we show that the first row power production increases with decreasing LLJ height. Due to the higher turbulence intensity, the wind turbine wakes recover faster in a neutral boundary layer than in a stably stratified one. However, for strong thermal stratification with a low-height LLJ, the wake recovery can be faster than for the neutral reference case as energy can be entrained from the LLJ. Flow visualizations reveal that under stable stratification the growth of wind farm's internal boundary layer is restricted and the wind flows around the wind farm. Wind farms extract energy from LLJs through wake meandering and turbulent entrainment depending on the LLJ height. Both effects are advantageous for wake recovery, which is beneficial for the performance of downwind turbines. This finding is confirmed by an energy budget analysis, which reveals a significant increase in the kinetic energy flux in the presence of a LLJ. The jet strength reduces as it passes through consecutive turbine rows. For strong stratification, the combined effect of buoyancy destruction and turbulence dissipation is larger than the turbulent entrainment. Therefore, the power production of turbines in the back of the wind farm is relatively low for strong atmospheric stratifications. We find that the pronounced wind veer in stably stratified boundary layers creates asymmetry in the available wind resource, which can only be studied in finite-size wind farm simulations. We emphasize that spanwise-infinite wind farm simulations may underpredict wind farm performance as the additional beneficial effect of LLJ cannot be observed.
AB - Low-level jets (LLJs) are the wind maxima in the lower regions of the atmosphere with a high wind energy potential. Here we use large-eddy simulations to study the effect of LLJ height on the flow dynamics in a wind farm with 10 × 4 turbines. We change the LLJ height and atmospheric thermal stratification by varying the surface cooling rate. We find that the first row power production is higher in the presence of a LLJ compared to a neutral reference case without LLJ. Besides, we show that the first row power production increases with decreasing LLJ height. Due to the higher turbulence intensity, the wind turbine wakes recover faster in a neutral boundary layer than in a stably stratified one. However, for strong thermal stratification with a low-height LLJ, the wake recovery can be faster than for the neutral reference case as energy can be entrained from the LLJ. Flow visualizations reveal that under stable stratification the growth of wind farm's internal boundary layer is restricted and the wind flows around the wind farm. Wind farms extract energy from LLJs through wake meandering and turbulent entrainment depending on the LLJ height. Both effects are advantageous for wake recovery, which is beneficial for the performance of downwind turbines. This finding is confirmed by an energy budget analysis, which reveals a significant increase in the kinetic energy flux in the presence of a LLJ. The jet strength reduces as it passes through consecutive turbine rows. For strong stratification, the combined effect of buoyancy destruction and turbulence dissipation is larger than the turbulent entrainment. Therefore, the power production of turbines in the back of the wind farm is relatively low for strong atmospheric stratifications. We find that the pronounced wind veer in stably stratified boundary layers creates asymmetry in the available wind resource, which can only be studied in finite-size wind farm simulations. We emphasize that spanwise-infinite wind farm simulations may underpredict wind farm performance as the additional beneficial effect of LLJ cannot be observed.
KW - wind farm
KW - wind turbine
KW - low-level jet
KW - Large eddy simulations
KW - wind energy
KW - renewable energy
KW - fluid dynamics
KW - fluid mechanics
KW - atmospheric boundary layer
UR - https://doi.org/10.1103/PhysRevFluids.6.014603
UR - http://www.scopus.com/inward/record.url?scp=85100185988&partnerID=8YFLogxK
U2 - 10.1103/PhysRevFluids.6.014603
DO - 10.1103/PhysRevFluids.6.014603
M3 - Article
VL - 6
JO - Physical review fluids
JF - Physical review fluids
SN - 2469-990X
IS - 1
M1 - 014603
ER -