Introducing the first self adapting aerodynamic surface

Bionic technology in its smartest application

learning from the role model of nature in applying next generation technology in wind energy.

AF-AX currently develops a surface technology for wind turbine rotor blades which is able to adapt the airfoil of the blade dynamically to the surrounding airflow by acting passively to the surrounding flow. By that it mimics the natural role model of a birds feather coating which by nature is equipped with the same feature to ensure high aerodynamic performance. Giving a rotor blade passive-dynamic reshaping abilities has the following benefits:

• Rotor blades will increase lift and reduce drag by that the power output
  of the turbine is significantly higher

• Stall resistant features ensure a fast spin up to react on any wind gust

• By its dynamic reshaping ability it has a highly turbulent robust
  feature ensuring permanent performance under almost any condition.

• Low wind sensitivity increases uptime and thus substantially more
  power gain over time.

Limits in current airfoil technology

Have you ever asked why birds don’t need runways and never fall from sky while we take so much effort creating huge infrastructures such as airports and air traffic control to maintain safety. Similar efforts are made in wind energy when aiming for a greater power output. Nevertheless, everything is based on one principle: airfoils that create lift. But our current means in improving performance of rotor blades or wings are on their edge – leaving many unsolved questions.

• Rotor blades have a limited operation range while creating high lift

• Turbulence is the most difficult situation for the blades leading to
  strong loss of lift and increase of drag

• Current state of the art rotor blades still create early flow separation
  leading to a higher starting inertia

• Smaller disturbance of the surface already increase drag significantly

… So the question remains why nature is not struggling with these problems.

Source of the problem: the rigid boundary condition on surfaces.

Fluid is a highly interactive mechanical construct which always tries to establish an internal mechanical solution. But when opposed to a rigid body like a rotor blade a different solution is created. As long all forces on the surface and in the fluid interact seamlessly together everything is fine. But when the body doesn’t represent the perfectly matching counterpart of the solution, an internal problem to the mechanical solution occurs forcing the fluid to produce a compensation by it’s own, which thus leads to turbulence.

Initial testing in the wind tunnel

Coming from a fluid dynamics simulation (CFD) background we initially just had the idea that feather like structures could tackle some of the problems above. But when doing further tests in a wind tunnel, it turned out that there are serious indications that our suggestions were right giving us stunning results we first didn’t believe by ourselves. A wing section we tested produced a cL factor of 2.01 and very good gliding angles (see report).

Transferring the wind tunnel results to an application

Encouraged by the positive result in the wind tunnel, we started the attempt to transfer the research results to an application on rotor blades. The first results were really disappointing. We extremely underestimated side-effects like centrifugal forces. But we didn’t lost our faith and continued to improve our prototype. Finally we could reproduce similar behaviors to those observed in the wind tunnel, again impressing us with unbelievably great results.

Nevertheless, we will still need to validate these results over time to eliminate any critics on the prototype and testing setup, so it can withstand a proper scientific proof soon. Stay tuned for further development news!

In any case, we believe that the improvements given by this technology can be tremendous – providing a disruptive spark to make wind energy an even more attractive investment in developing our future.