x Abu Dhabi, UAE Thursday 20 July 2017

Scientists plan RAK wind tunnel to test turbines

Research team from Ecole Polytechnique Federale de Lausanne already has 30m tunnel - now they plan one three times bigger in Ras al Khaimah.

Researchers in Switzerland plan to build a 100-metre wind tunnel with tiny model turbines to test how their configuration affects the velocity, turbulence, pressure and layer height of incoming wind. Courtesy of Ecole Polytechnique Fédérale de Lausanne (EPFL).
Researchers in Switzerland plan to build a 100-metre wind tunnel with tiny model turbines to test how their configuration affects the velocity, turbulence, pressure and layer height of incoming wind. Courtesy of Ecole Polytechnique Fédérale de Lausanne (EPFL).

LAUSANNE, SWITZERLAND //At one of the world's largest offshore wind farms, about 16 kilometres off the coast of Denmark, turbines catch enough breeze from the sea to produce power for 150,000 homes.

But researchers have questioned whether the alignment of the turbine - arranged with eight rows of 10 turbines in a large oblique rectangle - limits the amount of power it can generate.

Turbines harness the power of the wind; that is the point of them. But in doing so they sap it, leaving slow, turbulent air currents in their immediate wake.

Even when placed far apart, the turbulence can deeply affect the velocity or power of the wind received by other turbines and even other distant wind farms.

A research team at the Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland constructed a 30-metre wind tunnel for testing that relationship in an effort to make wind farms more efficient.

Using small-scale model turbines, they study how air flow in the lowest layer of the atmosphere - the first kilometre - would be affected by changes in temperature, pressure, humidity, air quality and the effects of wind farms.

Their research will eventually move to Ras Al Khaimah, where EPFL plans to build a wind tunnel more than three times the size, at 100 metres long, for its postgraduate research team in the emirate.

Inside it they could place models of cities, and differing topography, surface features, and simulate various atmospheric conditions such as ground or soil temperature.

"This will be a unique wind tunnel that will have features and capabilities that no other wind tunnel has," said Prof Fernando Porté- Agel, who is heading the research at EPFL's wind engineering and renewable energy lab. A second wind tunnel is also planned once that project is complete.

"Configuration of wind farms has not been studied enough, and in a wind tunnel we can play games with the distance between the turbines to see how different arrangements affect whether the power will start to increase or decrease."

Most of the turbines off Denmark's coast, for instance, wield only about 60 per cent as much energy as those in the front row.

"This is a big loss and very inefficient, basically because the fluid mechanics is not well understood," said Prof Porté-Agel.

Inside the Lausanne wind tunnel, researchers use light detection and ranging - a narrow laser beam - to measure distance, speed, rotation and concentration of wind after it passes through the 13cm turbines.

Fine wire anemometers are heated to slightly above the ambient temperature. Based on how quickly the wind cools the wire, they allow the researchers to gauge the wind speed. Cone-shaped pressure probes with tiny holes facing in various directions measure wind direction and static pressure.

All that data is crunched into a mathematical model, and used to build computer simulations of turbulent wind streams.

The goal is to create a system that can automatically determine the best placement of turbines at a specific site.

The simulations would show how a turbine might affect wind speed, turbulence and force, and at what range. While the computer simulations are already used, they require more statistics that can be gathered with full-scale experimental work.

Giacomo Valerio Iungo, a postdoctoral student who has worked on the wind tunnel projects in Lausanne, points to the importance of being able to test wake flows from the turbines themselves.

"There are so many things to consider connected to this," he said. "It is not just about temperature change, but meteorologically, we need to examine exchanges of heat, the water vapour from the ocean, everything that is connected."

Until now, research into wake flows has largely been the work of those interested in propulsive turbines such as those in jet engines, such as Nasa, the US space administration. As a consequence, it has tended to concentrate more on the blades' weight, design, material, angle and rotation rather than placement within a large-scale grid.

But the need to explore the properties of turbine arrays is only likely to grow as demand for wind power increases. In the US, the world's biggest producer of wind power, it is expected to account for about a fifth of the nation's electricity supply by 2030.

It is also gaining popularity in the UAE. Masdar, Abu Dhabi's clean energy company, recently completed foundations for what would be the world's biggest offshore wind farm in London's Thames Estuary.

Tasked with implementing Abu Dhabi's goal of getting 7 per cent of its power from renewable sources by 2020, Masdar has revised its strategy to include wind power, alongside solar energy.

"There will be, we hope, local projects that will be very relevant to emulate," said Prof Porté-Agel of the tunnels to be built in RAK. "It would be important to have in-house capability for this sort of thing."

The tunnel could also be used commercially by building planners, who need to know how wind is likely to erode a structure or affects its stability. Such assessment is required for every new building project, but this currently has to be done overseas.

Prof Porté-Agel plans to inquire about conducting tests on the 65m wind turbine producing energy on Sir Bani Yas Island off the western coast of Abu Dhabi.

The single turbine, brought to the island by Masdar and Abu Dhabi's Tourism Development and Investment Company, has a production capacity of 850 kilowatts per hour and since 2008 has been used to help power the island's facilities.

"Because the conditions here are so different, of course we would be very eager to test how the performance might be different," he said.

"It would be a unique opportunity."