A numerical model chain for flow simulation is being developed as part of the joint research project “WINSENT”. The chain will link large-scale weather models with small-scale flow models to produce a detailed chart of the circulation of the air – around the rotor blades, for example. Meteorological data which correspond to the model chain conditions in terms of space and time boundaries are required in order to be able to validate the individual models all the way along the chain.
The project partners – coordinated by the ZSW – will carry out measurements in intensive operation periods (IOP) at the research test site in order to collect these data. IOPs are periods of time in which all the available measuring instruments at the test site are used in a coordinated field campaign. The IOPs are scheduled before and after the research wind turbines are installed in order to be able to assess the impact of the wind turbines on the flow. The project partners include the Karlsruhe Institute of Technology (KIT), the University of Tübingen (Eberhard Karls Universität Tübingen), Esslingen University of Applied Sciences and the University of Stuttgart.
Autonomous measuring aircraft from the University of Tübingen will also be used alongside the masts which are fitted with the full complement of measuring instruments. The exchange of energy between the soil and the atmosphere will be measured at eddy covariance stations. Three laser optic lidar systems belonging to the ZSW and synchronised with space and time will measure the wind speed and wind direction.
The ZSW has a high-performance computing (HPC) cluster which is mainly used for numerical weather simulations and weather forecasts with the Weather Research and Forecasting (WRF) model. Global or regional weather model data are used as driving data or boundary conditions for the simulation and prognosis of the weather in a domain with a much higher resolution. Depending on the application, the spatial resolution is in the range of around 700 metres to around 50 m. Large eddy simulations (LES), methods for the numerical calculation of turbulent flows, are used if the spatial resolution is very high. The resulting meteorological simulation and forecast data are of a high spatial and temporal resolution and are used for various applications and fields of research.
The WRF data are used in the WINSENT project for the development and establishment of a wind test site in complex terrain where they serve as the first process step in a numerical model chain which is used to calculate the flow over the test site. Subsequent process steps in the model chain are carried out by the Esslingen University of Applied Sciences and the University of Stuttgart with CFD models in order to simulate the flow around wind turbines with a spatial resolution of up to a few centimetres. This allows the flow to be calculated on all scales right up to the turbulence at the tip of the wind turbine blades.
Boundary conditions specific to any given site, especially complex terrain, are taken into account in the WRF model in addition to the weather situation on the wider scale. This includes a high-resolution digital terrain model which records the location of the wind test site on the edge of a slope and identifies the different surface morphology of forests, meadows and fields and the seasonal fluctuations in the roughness of their surfaces due to the vegetation and the amount of foliage on the trees.
The WRF model is also used in the ParkCast project which is funded by the Federal Ministry for Economic Affairs and Energy (Bundesministerium für Wirtschaft und Energie - BWMi). The field of application in this case is offshore in the North Sea. The aim of the ParkCast project is to assimilate wind speed measurements with a long-range lidar device on the nacelle of a wind turbine in the WRF system and thereby significantly improve the high-resolution feed-in forecasts in the time range of up to one hour.