They disrupt the trailing edge eddies - which is what causes any noise - and so make them quieter. They are often fitted in areas where sound might be a particular issue.
They are surrounding a farm with hunners of cows in multiple fields, so I wonder if the noise is quite scary for them, hence efforts to make them quieter. Or the farmer insisting. Are they usually quite loud?
Most of the bird deaths are not actually physical strikes - it is a result of the massive change of air pressure as the blades pass at speed. Evidently painting one of the blades black - or some contrasting colour - keeps a lot of the birds well away.
I realise that I had mis-remembered this. It is primarily bat deaths that are caused by the air pressure changes around turbines - not birds. This is because bats have a particularly large and thin lung internal membranes which gives them high efficiency. The rapid decompression in the immediate wake of the turbine blades - particularly towards the tips, which are the fastest moving part of course - damages this membrane.
Birds have more compact lungs and hollow bones which aid in their breathing - a different solution to the efficiency problem and one that is not as susceptible to these pressure changes.
Could be. As is said so often: physics doesn't scale. Trailing edge eddies may not be the major source of the noise in this anyway - since these are pushing air not being pushed by it.
It reduces the turbulence at the trailing edge, reducing noise. Bernouli’s principle dictates that part of the force on the blade is due to the airflow on each side moving at different speeds, if the crashed into each other all at once, you’d get a lot of turbulence, and hence noise. The serrations ensure that the two flows meet over a longer distance, reducing said turbulence.
Riding my moped past these and I can tell you they make swooping noises, especially if they're aimed 90 degrees to you. These windmills are quite small and old, however, and are quite low. Its a bit intimidating seeing something that massive moving that fast, that close.
Add comment