Including realistic upper atmospheres in a wind-farm gravity-wave model

Abstract

Abstract. Recent research suggests that atmospheric gravity waves can affect offshore 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 a reference flow shows that internal gravity-wave resonance caused by the atmospheric non-uniformity can prohibit perturbations in the atmospheric boundary layer (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 1 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 16.6 % of the analyzed 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.

Large-eddy simulation of a 15 GW wind farm: Flow effects, energy budgets and comparison with wake models

“…Second, modeling the effect of this pressure distribution on the velocity field, e.g., by applying Bernoulli's principle. Information for modeling gravity wave induced pressure gradients in wind farms is provided by Smith (2009), Allaerts et al (2018), Allaerts and Meyers (2019), Lanzilao and Meyers (2021) and Devesse et al (2022). A wake model that considers the effect of streamwise pressure gradients was recently proposed by Dar and Porté-Agel (2022).…”

A mesoscale study of the occurrence and impact of wind farm blockage

“…The model approximates drastically the fluid dynamics at hub height (as a two-dimensional shallow-water model is used in the bottom layer), but it is nevertheless able to provide an upwind influence generated by the presence of gravity waves as a solution of an elliptic problem in the upper layer. Many numerical works have been performed in stratified conditions 14,15,16 providing observations and models useful to develop future corrections to assess how gravity waves affect the AEP. Numerical experiments have the luxury to be performed under prescribed stratification conditions.…”

A new parametrization of the Global Blockage Effect

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