Site specific simulation of ice shed and ice throw from wind turbines using ballistic models (EISBALL)
Project start: Mai 2018
Contact: Markus Drapalik
Wind energy will play a crucial role in the future Austrian energy mix. Currently, the increase in wind energy production is severely limited by the fact that most favorable areas have al-ready been put to use. Even the existing exchange of older plants with new, more efficient ones (repowering) at favorable sites is not sufficient with regard to the political objective. Thus, there is a heightened interest in technically more demanding sites, such as woodland and alpine areas.
The importance of risk assessments for ice shed or ice throw also increases with higher terrain complexity and/or icing frequency. These assessments usually rely on ballistic models to calculate shed or throw distances. However, the models currently used have significant weaknesses. The comparison between experiments and model calculations shows that no model can satisfactorily reproduce the shed distances. Furthermore, no reliability limits are given for the existing models, which means that for safety reasons considerably higher distances from wind power plants to infrastructures have to be selected. Finally, the applied simulation programs were mostly designed for flat or evenly inclined terrain; more complex terrains are not at all or at best poorly represented.
The present project is funded by the FFG under its energy research program and addresses these problems by developing a novel model including associated simulation tools. The data basis consists of observations and results from 1:1 experiments. The latter have the decisive advantage of allowing large sample numbers to be generated in a weather-independent manner- a prerequisite for statistically significant statements. In the experiments, test specimens are dropped or thrown from wind turbines. These specimens are based on 3D-scans of real ice fragments, which were found and digitized in previous pro-jects. With the aid of a 3D-printing process, these are reproduced with suitable density and in sufficient number. This is an entirely novel approach since no other actor in this research field has access to this method. The feasibility of these studies was demonstrated by the ISR in previous projects (Eisfall-Experimente, Urbane Windenergie – links) and suitable devices were developed.
The model itself is based on a model with six degrees of freedom (6DOF), allowing for all possibilities of translation and rotation. Compared to other models, additional forces from autorotation are taken into account in addition to the flow resistance. The necessary parameters are determined by computational fluid dynamics (CFD). The model is embedded in a simulation environment that takes into account both fractures of the ice fragments during the fall, as well as complex terrain.
The developed tool not only enables improved safety assessments, but also derivations for technological adaptations and optimization of wind turbines to specific site conditions. It should be emphasized that the improved safety assessments and validated limits for icefall and ice throw allow the development of new sites, which currently can only be used to a limited extent or not at all, due to excessively conservative safety distances.
WEB Windenergie AG – www.windenergie.at/
Energie Burgenland Windkraft – http://www.energieburgenland.at/oekoenergie/windkraft/unternehmen/kurzportraet.html