[annie123 (OP)]

On one of your recent programmes there was someone who said he had developed a device to fit to windmills etc to lower decibel level almost to nothing - modelled on owls' wings. But he did not go on to talk about how this was done. Can you get him to explain it somewhere?

[evan_au]

A study of noise suppression in an owl's wing identifies three mechanisms with specialised feathers at the  leading edge, trailing edge, and on the top surface.

Current wind turbine designs produce most of their noise at the trailing edge of the blade, especially on the downstroke. There are experiments underway trying to imitate aspects of an owls wing, such as by placing serrated edges on the trailing edge - see photos on page 15. (A similar scalloped edge may be seen around the engine outlets of recent high-efficiency/low noise jetliners).

A psychological view of equity also seem to play a role in noise perception - if a wind turbine is seen as something "done to" you, you will perceive any noise as being objectionable. However, if nearby residents receive some compensation, the noise is considered less objectionable.

[annie123 (OP)]

Thanks. Looks interesting. The guy on the programme didn't describe it.