Toroidal screwsA team of researchers from the Massachusetts Institute of Technology has experimentally selected the shape of a toroidal screw, which creates the lowest sound volume in the frequency range 1-5 kHz.
This is the most sensitive area for the human ear — babies cry and nasty multicopter motors squeal at this frequency. The latter has become an incentive for research – if people want to see a lot of useful drones around in the future, they should be quiet.
The toroidal propeller has blades in the form of a closed circle curved in two planes. There are a lot of variations in this design, the optimal bending parameters have yet to be found. The main thing is that such a blade has no beginning and no end, and therefore it moves evenly in the air. Because of this, there is no tension at the ends of the blades, the interaction of their parts with the air flow is the same everywhere, and therefore they are much less noisy.
Toroidal screws Prototypes of toroidal propellers are several times quieter than analogues with conventional blades — and in addition provide greater thrust.
Toroidal blades behave even better as part of boat propellers, where, in addition to noise reduction, the movement of water flows through the screw is stabilized. The boat rises slightly above the water, the friction is reduced – so an incredible 20% fuel economy is achieved.
Toroidal screws The disadvantage is obvious: it is not easy to make such a complex structure and it will cost very expensive.
For example, Sharrow Marine produces toroidal screws for motor boats at a price of $4,999 per piece, although a conventional screw costs no more than $ 500. And here the potential of 3D printing can be fully revealed, which will make it cheaper to produce toroidal blades for any industry.