Feedback and suggestions for the added-turbulence module of Floris v-3.5

[nzhtbyn]

We, at the Fluid Mechanics and Turbulence research group at Aarhus University, Denmark, recently had the opportunity to explore the latest version of Floris (v-3.5), and must say that we are impressed with the enhancements and improvements you have made. Your team’s dedication to advancing the field of modeling and control of wind farms is evident in the quality of your work.

We wanted to bring to your attention a particular aspect of the code that we believe could benefit from further refinement. Upon reviewing the “wake_turbulence” packages of the Floris v-3.5, we noticed a discrepancy in how the added turbulence through the formula suggested by Crespo and Hernández (1996) is being handled, where the turbine-induced added turbulence is positively proportional to the ambient turbulence level.

We are specifically referencing the code within the following files:

floris/floris/simulation/wake_turbulence/crespo_hernandez.py

Problem statement

We recently published a note titled “A short note on turbulence characteristics in wind-turbine wakes” which focused on the turbulence characteristics in wind-turbine wakes. The empirical study of Crespo and Hernández (1996), as highlighted in our work, showed that the turbulence added by the wind turbines is negatively proportional to the ambient turbulence level as $I_{+} = 0.73 a^{0.8325} I_0^{-0.0325} \left({x}/d_0\right)^{-0.32}$, where $I_0$, $a$, $x$, and $d_0$ denote the ambient turbulence intensity, axial induction factor of the turbine, the streamwise location, and the rotor diameter, respectively, and $I_+$ corresponds to the added turbulence intensity due to the presence of wind turbines.

We would like to respectfully recommend that you consider making the necessary corrections and refinements to ensure that your code accurately represents the physics involved in turbine wakes.

Impact quantification

To quantify the impact, we utilize the analytical-empirical Gaussian wake model proposed by Niayifar and Porte-Agel (2016) as the main framework with the original and the incorrect implementation for the turbine-induced added turbulence. We then apply the wake model to the Horns Rev 1 wind farm to evaluate the turbulence intensity within the farm in the full-wake condition.

The figure below depicts the turbulence intensity averaged across the rotor upstream of each turbine row, obtained from large-eddy simulations performed by Wu and Porte-Agel (2015), the correlation of Crespo and Hernández (1996), and its incorrect implementation (labeled as Eq. (2)). The layout of the HR1 wind farm is also shown in this figure on the right. We can see an absolute difference of 1.94% between the turbulence intensity of the waked turbines predicted by the correct and the incorrect added-turbulence formulation. The reason behind disagreement and further assessment can be found in the study of Zehtabiyan-Rezaie and Abkar (2023).

Figure: N. Zehtabiyan-Rezaie, M. Abkar, “A short note on turbulence characteristics in wind-turbine wakes”, Journal of Wind Engineering and Industrial Aerodynamics, vol. 240, p. 105504, 2023. 10.1016/j.jweia.2023.105504 - Copyright © 2023 by Elsevier.

References

@article{Crespo_Hernandez_1996,
author = {Crespo, A. and Hern{\'{a}}ndez, J.},
doi = {10.1016/0167-6105(95)00033-X},
journal = {Journal of Wind Engineering and Industrial Aerodynamics},
number = {1},
pages = {71--85},
title = {{Turbulence characteristics in wind-turbine wakes}},
volume = {61},
year = {1996}
}

@article{Zehtabiyan_Abkar_2023,
author = {Zehtabiyan-Rezaie, Navid and Abkar, Mahdi},
doi = {https://doi.org/10.1016/j.jweia.2023.105504},
journal = {Journal of Wind Engineering and Industrial Aerodynamics},
pages = {105504},
title = {{A short note on turbulence characteristics in wind-turbine wakes}},
volume = {240},
year = {2023}
}