Preprints
https://doi.org/10.5194/wes-2021-138
https://doi.org/10.5194/wes-2021-138
 
17 Feb 2022
17 Feb 2022
Status: this preprint is currently under review for the journal WES.

Extending the applicability of a wind-farm gravity-wave model to vertically non-uniform atmospheres

Koen Devesse1, Luca Lanzilao1, Sebastiaan Jamaer2, Nicole van Lipzig2, and Johan Meyers1 Koen Devesse et al.
  • 1Department of Mechanical Engineering, KU Leuven, Leuven, Belgium
  • 2Department of Earth and Environmental Sciences, KU Leuven, Leuven, Belgium

Abstract. Recent research suggests that atmospheric gravity waves can affect off-shore wind farm performance. A fast wind-farm boundary-layer model has been proposed to simulate the effects of these gravity waves on wind-farm operation by Allaerts and Meyers (2019). The current work extends the applicability of that model to free atmospheres in which wind and stability vary with altitude. We validate the model using reference cases from literature on mountain waves. Analysis of two reference flows shows that internal gravity wave resonance caused by the atmospheric non-uniformity can prohibit perturbations in the ABL at the wavelengths where it occurs. To determine the overall impact of the vertical variations in the atmospheric conditions on wind farm operation, we consider one year of operation of the Belgian–Dutch wind-farm cluster with the extended model. We find that this impact on individual flow cases is often of the same order of magnitude as the total flow perturbation. In 16.5 % of the analysed flows, the relative difference in upstream velocity reduction between uniform and non-uniform free atmospheres is more than 30 %. However, this impact is small when averaged over all cases. This suggests that variations in the atmospheric conditions should be taken into account when simulating wind-farm operation in specific atmospheric conditions.

Koen Devesse et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on wes-2021-138', Anonymous Referee #1, 03 Mar 2022
    • AC1: 'Reply on RC1', Koen Devesse, 09 May 2022
  • RC2: 'Comment on wes-2021-138', Anonymous Referee #2, 12 Mar 2022
    • AC2: 'Reply on RC2', Koen Devesse, 09 May 2022

Koen Devesse et al.

Koen Devesse et al.

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Short summary
Recent research suggests that offshore wind farms might form such a big obstacle to the wind, that the wind already slows down before it reaches the first turbines. Part of this phenomenon could be explained by gravity waves. Research on these gravity waves triggered by mountains and hills has found that variations in the atmospheric state with altitude can have a large effect on how they behave. This paper is the first to take the impact of those vertical variations into account for wind farms.