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.
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.
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.
Trailing edge you say? So not designed to mince up birds, that’s a relief.
Oh they’ll still mince birds, just with the blunt side
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.
So why don’t my CPU/case fans have serrated edges as well? Because they are too small?
Some do, e.g. Noctua: https://noctua.at/en/vortex-control-notches