This article describes a study in which modellers were challenged to compute the wind field at a forested site with moderately complex topography. The task was to model the wind field in stationary conditions with neutral stratification by using the wind velocity measured at 100 m at a metmast as the only reference. Detailed maps of terrain elevation and forest densities were provided as the only inputs, derived from airborne laser scans (ALSs) with a resolution of 10 m × 10 m covering an area of 50 km × 50 km, that closely match the actual forest and elevation of the site. The participants were free to apply their best practices for the simulation to decide the size of the domain, the value of the geostrophic wind, and every other modelling parameter. The comparison of the results with the measurements is shown for the vertical profiles of wind speed, shear, wind direction, and turbulent kinetic energy. The ALS-based data resulted in reasonable agreement of the wind profile and turbulence magnitude. The best performance was found to be that of large-eddy simulations using a very large domain. For the Reynolds-averaged Navier-Stokes type of models, the constants in the turbulence closure were shown to have a great influence on the yielded turbulence level, but were of much less importance for the wind speed profile. Of the variety of closure constants used by the participating modellers, the closure constants from Sogachev and Panferov (2006) proved to agree best with the measurements. Particularly the use of C µ ≈ 0.03 in the k-ε model obtained better agreement with turbulence level measurements. All except two participating models used the full detailed ground and forest information to model the forest, which is considered significant progress compared to previous conventional approaches. Overall, the article gives an overview of how well different types of models are able to capture the flow physics at a moderately complex forested site.Published by Copernicus Publications on behalf of the European Academy of Wind Energy e.V.
Abstract. This article describes a study where modellers were challenged to compute the wind at a forested site with moderately complex topography. The target was to match the measured wind profile at one exact location for three directions. The input to the modellers consisted of detailed information of forest densities and ground height derived from Airborne Laser Scans (ALS). All participating models except two used the full detailed ground and forest information to model the forest which is considered a significant progress. The ALS based data resulted in reasonable agreement of the wind profile and turbulence 5 magnitude. The best performance was found to be that of LES using a very large domain. For the RANS type of models the constants in the turbulence closure was shown to be of great significance for the turbulence level, but of much less importance for the wind speed profile. Overall, the article gives an overview of how well different types of models are able to capture the flow physics at a moderate complex forested site.
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