Improvement of Airflow Simulation by Refining the Inflow Wind Direction and Applying Atmospheric Stability for Onshore and Offshore Wind Farms Affected by Topography

Abstract

For this study, the annual frequency of atmospheric stability and the effects of topography were investigated, using ERA5 data and data from wind observation masts installed at four locations on an island for a site under development, where bidding will soon begin. As a result, we found that a variety of atmospheric stabilities appeared at the site, and that the annual average events were not neutral but, instead, unstable. Moreover, the deviation from neutral varied depending on wind direction and the wind speed varied greatly, depending on the mast position and wind direction. Additionally, it was necessary to reproduce the wind flow separation due to topography, in order to predict the wind conditions of wind turbines located close to the island. The accuracy of the airflow simulation by large eddy simulation was validated using the mast-to-mast wind speed ratio. For simulations, we used the commercial software RIAM-COMPACT, which has been widely used in Japan, as it allows the atmospheric stability to be freely set. As a result, we found that the accuracy could be improved by refining the inflow wind direction and taking the average of the results calculated under several atmospheric stability conditions.