Georges Darrieus (1888 - 1979) is a french engineer who has designed the patented vertical axis wind turbine fitted with NACA shape blades. The blades catch and harvest wind energy when going through the wind,
This technology is in the range of fast wind turbine (2<λ<5), that enable to work with high Reynolds numbers (> 10⁶). This permits to optimise the aerodynamic behaviour of the blade (high lift, low drag). The resulting lift-to-drag-ratio can easily reach a value of 20 which is tipically the range of ratio in aircraft, fan or large industrial wind turbines. This ratio enable to get correct efficiency of the system : the lift is the force that will speed up the rotor, although the drag is the force that will generates losses.
Thanks to this high Reynolds, number, the global efficiency of the wind turbine is improved compared to the "low speed wind turbine family" (savonius, windmill, western farm pumping wind turbines...) and the technology suits with efficient wind power harvesting solutions and electricity production. But large Reynolds number implies relative high blade speed and so high centrifugal forces.
In 1920, When Mr Darrieus developped the first prototype, the engineer uses cables and wood to make the blades, in a bowed shape called "troposkine". The centrifugal forces were correctly absorbed thanks to this shape.
Then the new high performance aluminium alloy permits to make the blades in a straight shape (H shape wind turbines), then in helicoidal shape thanks to composit, and now within an hyperboloidal shape using high density composit structures.
The advantage of the wind turbines is the global efficiency, that could theoritically reach 59%. The rotating speed enable to actuate directly a genrator, which is mandatory for electric energy production. And the architecture, with only one rotating part, without nacelle, make it suitable when maintenance is a criteria, for instance in decentralised energy production, or in offshore applications.
Comparatively to the Savonius wind turbine that shall be oversized to resist to tempests, the Darrieus wind turbine can be light, and better resists to high speed winds. Following the same calculation as for Savonius, a Darrieus wind turbine developping 1KW at 40km/h with an efficiency of 25% will have a wet area of approx 3m². assuming a rotor of 1.8m x 1.8m, fitted with thin blades with low drag, the 200km/h tempest will blow and generate a thrust of approx 1140Kg, a folding torque of 600N.m and it will require a brake of 20N.m.
For the same power, a Darrieus wind turbine will be much more light and the structure of the machine is downsized compared to Savonius system.