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Delegates are invited to meet and discuss with the poster presenters in this topic directly after the session 'Wakes: Do we need different models for onshore and offshore wind farms?' taking place on Wednesday, 12 March 2014 at 16:30 -18:00. The meet-the-authors will take place in the poster area.

Nikolaos Stergiannis 3E, Belgium
Co-authors:

(1) 3E, Brussels, Belgium (2) TEI, Kozani, Greece (3) Technological Educational Institue of Kozani, Kozani, Greece (4) NATIONAL TECHNICAL UNIVERSITY OF ATHENS, Athens, Greece (5) University of Western Macedonia, Kozani, Greece (6) National Technical University of Athens, Athens, (7) InFlow E.E., Athens, Greece

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Abstract

CFD modelling approaches of onshore wind farms with different turbulence intensities and their potential impact on the microclimate of Chios

Introduction

At the islands of the Aegean Sea in Greece, during the last years, there is a plan for a big project development of large scale wind farms. Moreover, the island of Chios has a uniqueness because of the mastic trees, which are sensitive in temperature changes. Within the European Union, mastic production in Chios is granted protected designation of origin. In order to protect this unique and precious for the local economy product, further studies for the potential impact of wind farms on microclimate of the island have to be done.

Approach

In the current project a CFD simulation of a large scale wind farm takes place. The analysis is carried out with the use of the commercial CFD code ANSYS Fluent. Steady state computations of full 3D Navier-Stokes equations, using the k-ε turbulence closure scheme appropriately parameterized for atmospheric flows are carried out. Two different turbulence intensities are tested, 8% and 15%.

Main body of abstract

The island's mastic production is controlled by a co-operative of medieval villages, collectively known as the "Mastichochoria", which are located in southern Chios. Therefore, for this study, it is considered the worst case scenario which assumes a wind direction that comes from the North and a flat terrain. In order to examine the presence of the wind farm, we are studying the development of the multiple wake effects downstream. As already mentioned, the worst case scenario would be the one with a flat terrain and with a small turbulence intensity (8%) to ensure that we benefit the wake development and that we increased the length of these phenomena downstream without the presence of the complex terrain. Simulating a wind farm with more than one fully detailed wind turbines and possibly complex terrain geometry requires significant computational power and time. For this reason the turbine rotors are approximated as discs which behave as momentum sinks and this is the approach that has been adopted in the present study.

Conclusion

It is concluded that the impact of the wind farms on the microclimate is:
- increased within an atmospheric boundary layer of reduced turbulence, as it was expected, since a less mixed atmosphere increases the wind turbine wake effects downstream of the rotor,
- reduced with the distance as the k, production term of turbulence and main factor of the atmospheric mixing, is normalized with the lateral flow after 8km.
Especially for this case, "Mastichochoria" are located in a distance of 10km to 25km downstream of the wind farms and an impact on the microclimate at that distance is not expected.



Learning objectives
CFD simulation of Wind Farms. Evaluation study of multiple wake effects development. Impact of turbulence intensity at the wake development. Impact of wind farms on microclimate.