Large eddy simulation study of the humidity variation in the shadow of a large wind farm

TL;DR

This study uses large eddy simulations to analyze how relative humidity varies downstream of a large wind farm, revealing persistent humidity changes and layout effects on humidity distribution.

Contribution

It investigates the downstream development of humidity variations caused by wind farm wakes using LES, comparing aligned and staggered layouts in a stable atmospheric boundary layer.

Findings

Humidity decreases below hub height within the farm

Humidity increases above hub height within the farm

Staggered layout maintains elongated low humidity regions better

Abstract

Numerous studies have shown that wind turbine wakes within a large wind farm bring about changes to both the dynamics and thermodynamics of the atmospheric boundary layers (ABL). Previously, we investigated the relative humidity budget within a wind farm via field measurements in the near-wake region and large eddy simulations (LES). The effect of the compounding wakes within a large wind farm on the relative humidity was also investigated by LES. In this study, we investigate how the areas of relative humidity variation, that was observed in the near-wake, develop downstream in the shadow region of a large wind farm. To this end, LES of a wind farm consisting of 8x6 wind turbines with periodic boundary condition in the lateral direction (inferring an infinitely wide farm) interacting with a stable ABL is carried out. Two wind farm layouts, aligned and staggered, are considered in the analysis and the results from both configurations are compared to each other. It is observed that a decrease of relative humidity underneath the hub height and an increase above the hub height build up within the wind farm, and are maintained in the downstream of the farm for long distances. The staggered farm layout is more effective in keeping a more elongated region of low relative humidity underneath the hub, when compared to the aligned layout.