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.

Highlights

  • In recent years, it has been well documented that wind farms form a blockage to the flow in and around them (Bleeg et al, 15 2018), thereby displacing the Atmospheric Boundary Layer (ABL)

  • Such displacements can propagate through the overlying inversion layer and free atmosphere as waves in stably stratified atmospheres, conditions which frequently occur at sea

  • By combining these cases with the atmospheric profiles analyzed in previous sections, we investigate the effect of vertical variations in the

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Summary

Introduction

It has been well documented that wind farms form a blockage to the flow in and around them (Bleeg et al, 15 2018), thereby displacing the Atmospheric Boundary Layer (ABL). Such displacements can propagate through the overlying inversion layer and free atmosphere as waves in stably stratified atmospheres, conditions which frequently occur at sea. 20 Previous work on the interaction between gravity waves and wind farms has assumed the free atmosphere to be uniformly stratified, with a constant background wind (Smith, 2010; Allaerts and Meyers, 2017, 2019).

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