Enhancing Wind Energy Assessment and Optimization through Airborne Observations: Insights from Onshore and Offshore Measurements

Abstract

The expansion of wind energy is set to increase significantly over the next few years. This will lead to challenges both onshore and offshore, such as the influence of wind farms on downstream wind farms in the German Bight or the change of the wind field of wind turbines in complex terrain. This thesis investigates the influence of orography on the wind field in a wind energy test site in the Swabian Alb and the effects of wakes from large wind farm clusters on downstream wind turbines in the German Bight. The measurements carried out with crewed and uncrewed aerial systems (UAS) are also used to validate and compare model data. Complex terrain, such as small hills or the edges of slopes, changes the flow considerably. Above the highest point of the obstacle, there is an increase in wind speed, known as a speed-up. In addition, recirculation zones can form downstream of the elevation.Both of these often lead to strong shear (turbulence) at the boundary between the flow that is accelerated by the slope and the flow that is slowed down below it. The lower part of modern wind turbines is usually located in this height range. The roughness of the slope surface also has an effect. For example, if the slope is overgrown with forest, this will further increase turbulence and flow velocity and therefore affect the yield and life time of wind turbines in such areas. In this work, flight measurements with the UAS MASC-3 (Multi-Purpose Airborne Sensor Carrier, Version 3) are presented to analyse the wind field over a 200~m high slope and compared with a model chain consisting of a WRF (Weather Research and Forecast) model and an openFOAM (Open Source Field Operation and Manipulation) model. The results show that there is a significant increase in wind speed over the highest point of the west-facing slope, in the area of the future research wind turbines (FWEA). The resulting shear also increases the turbulent kinetic energy (TKE) at the lowest measurement heights many times compared to the undisturbed flow at 200 m above ground. The seasonal influence, i.e. the presence or absence of foliage cover on the slope, is clearly evident. Both velocity and TKE are higher in summer. The model chain simulated the wind field above the slope edge in two case studies with good agreement. Based on flight measurements with the crewed aircraft D-IBUF of the TU Braunschweig over the German Bight to investigate the wake effects of large wind farm clusters and their influence on downstream wind farms, the industrial model FOXES (Farm Optimisation and eXtended yield Evaluation Software) is compared in different configurations. The measurement results show clearly pronounced wake effects under stable atmospheric conditions. In comparison, the simulation results show good results in the immediate vicinity downstream of the wind farm clusters. The model quality decreases with increasing distance to the wind farms.

Die Dissertation ist gesperrt bis zum 31. Dezember 2024 !