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Discussion Starter #1
I don't know if anyone has noticed but Comair-Rotron fans are the only fans to feature strange notches on the trailing edge of their blades:

https://assets.suredone.com/1720/media-photos/pq24c0x-comair-rotron-24vdc-fan-pq24c0x-new-2.jpg

Apparently Comair-Rotron has a patent on this and it's goal is to reduce fan noise:
'A fan for moving a gaseous fluid, e.g., air, is described in which the high audible frequency noise resulting from the phenomenon occurring at the trailing edges of the blades, known as vortex shedding, is reduced. This is accomplished by notching an edge of each of the blades so that the pattern of vortices leaving the blade, which causes the noise, is disturbed and a turbulence condition engendered. The turbulence distributes the pressure fluctuations resulting from movement of the blades through the fluid over a relatively broad band of frequencies and reduces the annoying noise frequencies. Various notch configurations are disclosed.'
 

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not same concept as the jagged edges on GT's blades?


 

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Discussion Starter #3
The comair-rotron fans have the notches at the trailing edge near the tips of the fan blades:
 

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There are many ways of reducing fan blade turbulence and noise. bequiet uses their ribbed fan blades. Noctua has their stepped inlet, inner surface microstructures, flow acceleration channels, etc. Silverstone's older fans had a golf ball pattern to reduce noise. The old Scythe Grand Flex had the notches near the base of the blades and ribs around the interior of the frame, and the list goes on.
 

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Discussion Starter #5
There are many ways of reducing fan blade turbulence and noise. bequiet uses their ribbed fan blades. Noctua has their stepped inlet, inner surface microstructures, flow acceleration channels, etc. Silverstone's older fans had a golf ball pattern to reduce noise. The old Scythe Grand Flex had the notches near the base of the blades and ribs around the interior of the frame, and the list goes on.
I wonder if any of these techniques really work? I'm surprised that Comair-Rotron bothers, most of the big industrial fan manfacturers don't seem to care about noise (e.g. SanAce, Delta, Sunon).
 
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