Quieter turbines

Noisy wind turbines are a problem. Not only for the residents who live next to them, but for their operators too.

If wind turbines clatter and whistle too loudly, they may only operate under partial load to protect residents living near them - but this also means they produce less power.

Now, German researchers have come up with a solution to the problem - they have developed an active damping system that cancels out the noise by producing counter-vibrations.

One source of noise from a wind turbine is from the gears that vibrate in the gearbox. These humming sounds are relayed to the tower of the wind turbine where they are emitted across a wide area.

'People find these monotone sounds particularly unpleasant, rather like the whining of a mosquito,' said André Illgen, a research associate at the Fraunhofer Institute for Machine Tools and Forming Technology in Dresden.

Passive damping systems have been used to address the issue, but the effectiveness of the systems has been somewhat limited: they only absorb noise at a certain frequency.

This is a problem as modern wind turbines adapt their rotational speed to the wind velocity to generate as much electricity as possible, meaning the frequency of the humming sound can vary too.

The Fraunhofer IWU researchers’ active damping system on the other hand has been developed to react autonomously to any change in frequency and damp the noise regardless of how fast the wind generator is turning.

The system itself comprises a number of piezo actuators that constantly measure the vibrations arising in the gearbox. These pass their results to a system that controls a number of actuators that counter the vibrations that are created, cancelling them out.

The researchers have already developed a working model of the active vibration damping system, and their next step will be to perform field trials.