CFD modelling approaches of onshore wind farms PO. ID and their potential impact on the microclimate of Chios 132 N.A.Stergiannis1,2, K.G.Rados3,5, G.Caralis4, C.Lacor1, R.Donnelly2, A.Tourlidakis5, I.Perivolaris6, A.Zervos4 (1) Vrije Universiteit Brussel, Belgium (2) 3E Brussels, Belgium (3) Technological Educational Institute of Kozani, Greece (4) National Technical University of Athens, Greece (5) University of Western Macedonia, Greece (6) InFlow E.E, Greece In memory of professor Konstantinos G. Rados (1965-2013) Abstract CFD Modeling Approaches Wind energy is one of the fastest growing industries worldwide. Wind farms are rapidly growing in 1. Turbulence modeling: modification of k-ε constants for atmospheric flows [6,7] size and numbers all over the world [1]. As these numbers increasing and most of the growth being in C =0.033, C =1.12, C =1.83, σ =1.0, σ =1.3 large wind farms that are often located on agricultural and near residential communities questions μ ε1 ε2 k ε regarding the possible impacts of such wind farms on global and local weather and climate are 2. Inlet conditions: Monin-Obukhov similarity equations [4,5] generated. Temperature data from a wind farm at San Gorgonio, California, collected during June 18– 0.5 0.5 2 3 August 9, 1989 and studied after by Somnath Baidya Roy and Justin J. Traiteur [2] show that large u* f u* f u* z z k z z f u0 z ln 5 scale wind farms can significantly affect near-surface air temperatures. These effects result from 0 0 z L Cm fm z fm 0 enhanced vertical mixing due to turbulence generated by wind turbine rotors. Recent modeling z z studies agree that wind farms can significantly affect local-scale meteorology [4, 5]. However, these f 1 4 f 1 5 studies are based only on model simulations and are not validated against observational evidence. L m L During the last years in Greece there is a plan for a big project development of large scale wind farms at the islands of the Aegean Sea. Moreover, the island of Chios has a uniqueness, the mastic trees. 3. Wind turbine modelling in the 3D Navier-Stokes solver [6] Though there a many varieties of mastic trees growing throughout the Mediterranean, it is on the F 0.5U 2 C A Greek island of Chios that the production of gum mastic is centered with its Pistacia lentiscus chia ref T variety. Within the European Union, mastic production in Chios is granted protected designation of origin. 4. A reference wind speed (Uref)of 8 m/s has been used. In order to protect this unique and precious for the local economy product, further studies for the Results installation of a large wind farm with respect to the local microclimate of the island have to be done. The island's mastic production is controlled by a co-operative of medieval villages, collectively Turbulence Intensity 8% Turbulence Intensity15% known as the "Mastichochoria", located in southern Chios, 15 km downstream of the proposed wind farm location. Therefore, for this study, it is considered the worst case scenario, with respect to the k turbulence k turbulence wake development, which assumes: • a wind direction that comes from the North, • a flat terrain and • a small turbulence intensity (8%) Simulating a wind farm with more than one fully detailed wind turbines and possibly complex terrain geometry requires significant computational power and time. In line with this, the wind turbine rotors are approximated as single actuator disks (momentum sinks). Why do we care? velocity velocity • Chios is well known for the production of mastic, from which it derives its name. • Mastic is the hardened resin of the mastichodentra (mastic tree) and is only harvested on Chios • The cultivation is only accomplished in the South part of Chios, due to the dry and hot climate • Total cultivated area 20 km2 (~12% of the total cultivated are) – 2 millions trees - 4.500 agricultural families engaged • Major part of the local economy, price of mastic is 72 €/kg • Annual production ~ 150 tn Top view – k turb at HUB height Top view – k turb at HUB height Project under investigation Side view – k turb at 1 km downstream Side view – k turb at 1 km downstream Aigaia Zefxi 706MW – 28 wind farms (Lesvos, Chios, Lemnos) Side view – 5 km downstream Side view – 5 km downstream Side view –10 km downstream Side view –10 km downstream Wind turbines 2MW and D=80m Conclusions 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 and as it was also observed at [2]. • reduced with the distance as TKE is normalized with the lateral flow after 8km. Lesvos: 10 wind farms (306MW) Mastichochoria are located in a distance of more than 15 km downstream of the wind farm and Chios: 7 wind farms (150MW) no impact on the microclimate is expected at that distance as it was showed on the results. Lemnos: 11 wind farms (250MW) More and above by taking into consideration the complex terrain of Chios and the altitude difference between Mastichochoria and the wind farm under investigation we can clearly declare Methodology that the wind turbines will not affect the mastichodentra (mastic trees). As showed in [2] the impacts of wind farms on local weather can be minimized by siting wind farms in regions with CFD simulations of a large scale wind farm under development in Chios take place. The analysis is high natural turbulence. 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 Far from that we should be more concerned and further investigate the impact of the upcoming atmospheric flows are carried out. Two different turbulence intensities are tested, 8% and 15%. Greenhouse effect to the mastichodentra and to other agricultural products. The size of the computational domain is 7km wide, 800m height and 34.4km length. The multiblock References mesh (~14M hexahedral elements) was created in ICEM. The layout of the wind farm was designed according to the original positioning of the wind turbines. 1. GWEC, Global Annual Installed Wind Capacity 1996-2012 2. Baidya Roy S. (2011), .Simulating impacts of wind farms on local hydrometeorology., J.Wind Eng. Ind. Aerodyn., doi:10.1016/j.jweia.2010.12.013. 3. Baidya Roy S.B. and Traiteur J.J. (2010), .Impact of wind farms on surface air temperatures., Proc. Natl. Acad. Sci. doi:10.1073/pnas.1000493107. 4. Baidya Roy S, Pacala SW, Walko RL (2004) Can large wind farms affect local meteorology? J Geophys Res 109:D19101 10.1029/2004JD004763. 5. Adams AS, Keith DW (2007) Wind energy and climate: Modeling the atmospheric impacts of wind energy turbines. EOS Trans AGU 88 Fall Meeting Suppl. 6. J. M. Prospathopoulos, E. S. Politis, K. G. Rados, P. K. Chaviaropoulos (2011), “Evaluation of the effects of turbulence model enhancements on wind turbine wake predictions”, Wind Energy, Vol 14, pp 285-300. 7. Prospathopoulos J.M., Politis E.S., Chaviaropoulos P.K., “Modelling Wind Turbine Wakes in Complex Terrain”, Proc. European Wind Energy Conference, Brussels, EWEC, 2008. EWEA 2014, Barcelona, Spain: Europe’s Premier Wind Energy Event.