Current tall wind turbines are often placed in remote areas on steep ridges and in forested terrain. This work package aims to provide a detailed and accurate description of the wind flow at selected sites in such terrain based on well-instrumented meteorological field experiments covering a wide range of topographical and climatological conditions. The produced data will be public available and can be used by private and public partners to develop models and engineering tools.
Experiments in WP 2
Northern Europe combined mesoscale experiment
This activity is a true integration and coordination of national efforts. It integrates efforts in Germany, Denmark, Sweden and Latvia. The purpose of the experiment is to validate mesoscale models, both statistics and short-term prediction and more detailed models of coastal regions. The experiment maps near shore wind resources (0-10 km with lidars on the coast, 0-100km with conically scanning lidars on ferries, several masts both on- and off-shore). It should also be used to assess downscaling to wind turbine relevant heights and to assess the potential benefits of assimilation of wind data into short-term prediction models. The experiment will play an important role in the use of offshore satellite data.
More detailed description of the mesoscale experiment
Aim of the experiment is to produce a dataset for the validation of meso-scale models applied to coastal and offshore regions, possibly with additional and more detailed data close to the land-sea discontinuity that are also suitable for a comparison with micro-scale model outputs.
IWES will combine a LiDAR measurement for the vertical wind profile from a ship that is travelling on a regular route from one cost to the other (e.g. a ferry line, already tested by IWES) with long-range scanning LiDAR devices.
DTU has obtained funding for an experiment to scan near coastal wind resources with pulsed wind lidars. NEWA can supplement this experiment and the data should be shared. DTU has several masts up to 160 m at Høvsøre, less than 2 km from the North Sea.
Several tall mast operated in the region will supplement the experiment. These include several tall masts owned by the Latvian military along the Latvian coast that could be instrumented by the project.
Sweden has many tall meteorological towers. A new 180 m tall mast somewhat further inland will be erected in the fall. An intensive campaign with remote sensing instruments is also planned at the site in which the 180 m tall mast will be erected. The aim is to better understand the horizontal variability of the vertical structure of the atmosphere over patchy forests.
Forested hill experiment in Kassel
Centred around the existing 200 m mast of Fraunhofer IWES at Rödeser Berg near Kassel an experiment on patchy forest over hilly terrain will be conducted. The Forested Hill Experiment will comprise long term mast based measurements of at least one year. These will be complemented by an intensive measurement campaign of several months using multiple lidars and scanning lidars.
The uncertainty in the estimation of flow characteristics is notoriously high in this kind of terrain and the modelling of the flow is at the forefront of research. Thus, the Forested Hill Experiment at the site near Kassel will provide highly valuable data sets to meso- and micro-scale modellers. A large variety of instrumentation – including sonic anemometers and a ceilometer allow investigations to model performance with regards to atmospheric stability, boundary layer structure and seasonality among others.
Double hill experiment at Perdigao
The purpose of this experiment is to study how an upstream hill with flow separation affects the mean wind speed and turbulence at a down-stream hill. We shall also investigate how and if the presence of a turbine on the upstream hill will affect the flow separation behind the hill.
Forwind will support the experiment with up to three scanning long range lidars. In this experiment there is a strong interest in participation from American colleagues from NCAR, Notre Dame University and other universities.
The experimental apparatus shall comprise three 100 m masts plus circa ten masts with height varying between 60 and 80 m able to receive equipment from partners and fitter with energy supply and data collection systems. Short term campaigns are also foreseen using meteorological balloons.
Complex terrain experiment with a strong mesoscale component at Alaiz
The focus of this experiment is testing of the model chain in complex terrain in an area with strong mesoscale variability. We will perform an experiment where the existing tall masts at the site are supplemented with a row of masts extending northwards to an upstream ridge. This row will be supplemented with ordinary conically scanning lidars as well as long-range scanning lidars.
A systematic evaluation of the model-chain from mesoscale to microscale is proposed with focus on the Alaiz mountain where CENER's Test Site is based as well as several operating wind farms from Acciona. The focus area is about 30x30 km and suitable for the study of high-resolution mesoscale-to-microscale models with strong coupling between terrain and thermal stratification.
At mesoscale level it is worth studying the link between the synoptic activity along the Ebro valley with the regional wind climate and with the mountain flows. A network of more than 700 surface stations along the Ebro valley will be used to study the wind climatology and its role in the flow behaviour around the Alaiz mountain.
Large-eddy simulations for additional idealized test cases and experimental sites
Additional numerical experiments with a large-eddy simulation model offer the possibility to obtain spatially and temporally highly resolved data under controlled environmental conditions. One objective of the application of large-eddy simulation models in this task is the generation of additional data sets for less complex test cases than the experimental ones that can be used for the verification of meso- and microscale models. E.g., to complement the „Northern Europe combined Mesoscale Experiment“, the development of internal boundary layers in cases of land-sea or sea-land transitions shall be simulated with LES, where the complexity of the real coastline and processes in the atmospheric boundary layer is reduced by prescribing a straight-line boundary between land and sea.
The land-sea transition will be prescribed as a step change in roughness and surface temperature. Simulations will include situations with the development of low-level jets for an offshore oriented flow. Low level jet events are extremely important for wind energy applications, as strong wind speeds come along with strong vertical shear of the wind profile and comparatively high turbulence levels in these events.