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Unraveling turbulence at the Wind Engineering and Renewable Energy Lab Share Share

With funding from the Emirate of Ras Al Khaimah, students and researchers at EPFL and EPFL Middle East are developing tools to optimize wind farm design for renewable energy production.


Could you stop the wind altogether by setting up too many wind turbines? Not under any realistic circumstances! But understanding the complex interaction between wind and wind turbines is no simple matter. Even if the wind flows smoothly before passing through a turbine, it comes out the other side in a complex collage of whorls, from large to small to tiny. The turbulence thereby created is - and has been been for centuries - one of physics’ outstanding problems. And with the prospect of expanding wind farm capacity around the world, understanding it is becoming increasingly important. 


“If you set up a wind turbine for electricity generation in one location, you have to ask yourself where to set up a second one to maximize power output,” says Fernando Porté-Agel, head of the Wind Engineering and Renewable Energy Lab (WIRE), an EPFL Middle East partner lab. “Given the atmospheric circulation - the wind - that prevails in a region, where should you build your wind farm? On a hilltop? In the bottom of a valley? And what is the optimal arrangement of wind turbines? It’s all about finding the right density and distribution of wind turbines, so that the wind farm can be as efficient as possible,” he says. 


Experiments and simulation go hand in hand

At WIRE, experimentation and numerical simulation go hand in hand. Fernando Porté-Agel and the students and researchers he works with use experimental results to develop and improve tools for simulating turbulent flows on supercomputers. They are interested in learning more about how turbulence transports momentum as well as scalars, such as heat, temperature, pollution, dust, or sand. The computer models, once validated, can then be used to optimize wind farm design. 


Validation involves comparing simulation results to vast sets of experimental data. Using miniature windmills, about as tall as a hand, Porté-Agel’s students are testing a wide range of wind farm geometries in EPFL’s wind tunnel - a long corridor run through by a constant wind, driven by a huge fan at one end. Instruments strewn throughout the tunnel measure wind speed and direction, temperature, pressure, and other parameters, and cameras help visualize the whorls formed as the wind passes through the tunnel. 


At the same time, in a unique experimental campaign, other group members are measuring the turbulence created by an actual wind turbine, located in the narrow Upper Rhone Valley near Martigny, Switzerland. Using two lasers set up on either side of the wind turbine, they have been able to gather extremely high resolution data, capturing the variability common to real-world settings. 


These data help test and improve the numerical models being developed in the lab. To simulate the air that flows through a wind farm, the researchers need an accurate understanding of the wind in the lower atmosphere, within the so-called atmospheric boundary layer. Their models must capture the motion of the rotors as they slice through the wind blowing through them. And they need to be able to account for local topography and the wind’s variability as it blows over the wind farm. 


EPFL Middle East Master’s students

As part of the joint Master’s program between EPFL and EPFL Middle East on Energy Management and Sustainability (MES), WIRE is currently hosting 7 Master’s students that are actively investigating into each of these issues. Supervised by PhD students and postdocs, 3 are modeling the wind over  wind farms at different scales using a variety of computational platforms, from an in-house Large Eddy Simulation (LES) code, to commercial software such as Fluent, and WRF, an open source meteorological model. At the same time, their peers are improving the setup and execution of the experiments in the wind tunnel and outdoors. 


“It’s a real lesson in interdisciplinary collaboration,” says Sina Shamsoddin, a Master's student at WIRE. Just the kind that will be needed to successfully set up wind farms around the world - and in the Middle East. Besides potential applications in the UAE, expertise in this field will become increasingly valuable throughout GCC countries and the region at large, from Iran to Eastern Africa.  



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