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For further information, please contact:
Olivier Auguy
Fläkt Solyvent-Ventec
+33 472 451 453
olivier.auguy@flaktwoods.com
Anders Mårtensson
Global Communications Manager, Fläkt Woods Group
+46 36 193 330
anders.martensson@flaktwoods.com
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Fläkt Woods has completed refurbishment work on what is believed to be the world’s largest fan, part of the giant S1MA, the largest transonic wind tunnel in the world, located at the ONERA facility in Modane, France.
Over the last 50 years aerospace testing has been so extensive at the ONERA research agency, that even though the giant S1MA wind tunnel has been continuously maintained and modernised, a major upgrade was required. The bulk of the work involved replacing the two giant counter-rotating fans, (15 m in diameter, weighing 58 tons per impeller and requiring 88 MW power), the fans comprise 12 blades upstream and 10 blades downstream respectively.
In order to verify the state of the impellers, aerodynamic calculation of the flow field through the blades was necessary, and this was difficult to achieve, requiring millions of mesh points for Navier-Stokes computation. For this application, ONERA used CFD analysis. Once a report on their state was complete, ONERA invited tenders for their replacement.
One company stood out to win the contract with a proven track record of constructing and refurbishing the largest fans in the world, Fläkt Woods. The contract to replace impellers was awarded to the Company after engineers demonstrated detailed solutions to overcome the problems of wear and tear of the blades.
One suggestion included use of composites substitutes, which Fläkt Woods, a leader in this field, calculated would offer significant advantages to metals due to the flexibility of selecting various combinations of glass, Kevlar, carbon reinforcement and resin matrix. It was demonstrated that weight savings of over 27% could be made using these products.
However, because of the history of using metal and the cost implications of composites, the decision was taken to replace the existing steel fabricated blades with a new steel blade design, optimised to reduce peak stress level to half the previous level and using high strength steel in the blades construction, with double the original strength.
After nearly 4 years of extensive work, the project is now complete, with the supply and the installation of new impellers. As a major benefit, energy savings above 10% are obtained.
History of the S1MA
The wind tunnel S1MA is the largest transonic wind tunnel in the world. It was originally used primarily by the French aerospace community, and since the early 1990s the wind tunnels have attracted an increasing number of international users.
Today, ONERA enjoys a host of industrial clients from all over the world. An example of this is the fact that every aircraft in the Airbus family has ‘flown’ in one or more of the ONERA wind tunnels. The tunnel is equipped with two counter rotating fans, driven by Pelton turbines. The minimum time to bring up the speed from Mach 0 to Mach 0.8 is 3 minutes with speeds of up to Mach 1. The tunnel’s blueprint forms a circuit comprising a rectangle 155 m long and 40 m wide, with a maximum diameter of 24 m and a test section diameter of 8 m.
Surprising power source
S1MA also has a unique power source. Its fan is driven directly by a channelled waterfall 850 m in height. In fact, this is precisely why the test centre was built in Modane, in order to benefit from the hydropower provided by the large quantities of water stored in artificial lakes in this mountainous region.
The water is delivered via pressure line from the Aussois dams and drives two Pelton water turbines, one fitted to each stage of the two-stage fan. 32 million tons of water has passed through the turbine for A380 tests.
What is a wind tunnel?
When an aircraft moves through calm air, its aerodynamic behaviour is the same as if it was immobile and the air was rushing past it. A wind tunnel is a test facility used to generate a flow of air past a scaled model of an aircraft. It provides various measurements to determine aerodynamic behaviour and performance. In that respect a wind tunnel can be seen as an ‘aerodynamic flight simulator’.
Although actual flight testing is more realistic, the advantages of the wind tunnel are obvious. Wind tunnel testing can be performed at an early stage in an aircraft development programme without having to wait for the first prototype. The costs are clearly lower and the risks, both technical and safety-related, are far less severe than those associated with a real flight test.
A wind tunnel can provide intermittent or continuous airflow, running from as little as a fraction of a second to several hours, and at high or low speeds to simulate take off and landing conditions or cruise conditions. It can be of the open circuit type where the airflow leaving the tunnel does not re-enter the circuit or of the closed circuit type where the same air is re-circulated. Finally, it can be pressurised, or can operate under normal atmospheric pressure. The ONERA S1MA wind tunnel is a continuous, high speed, closed circuit, atmospheric test facility.
ONERA
ONERA (Office National d’Etudes et de Recherches Aérospatiales) is the French aerospace research agency, operating under the auspices of the Ministry of Defence. Its prime mission is to direct and oversee aerospace research, and transfer this research to industry.
ONERA manages the largest fleet of wind tunnels in Europe. It has 2,000 employees, including 1,000 scientists and engineers, and operates through eight main facilities in France. In particular, ONERA conducts research in the disciplines and techniques involved in design of an aircraft or spacecraft: aerodynamics, flight dynamics, energetics, structural strength, materials, optics and laser, acoustics, radar and electromagnetism, electronics, systems, robotics, information processing.
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