These strangely-shaped twisted-toroid propellers are a revolutionary (sorry) advance for the aviation and marine sectors. Radically quieter than traditional propellers in both air and water, they're also showing some huge efficiency gains.
Propeller design hasn't really changed over the past century but the clever boffins at MIT's Lincoln Laboratory have come up with a radical new design after wondering whether prop noise could be mitigated with differently-shaped propellers.
"We came up with this initial concept of using a toroidal shape, this annular wing shape, to hopefully make a quieter propeller," says Dr. Thomas Sebastian, a senior staff member in the Lincoln Lab's Structural and Thermal-Fluids Engineering Group.
Within a few attempts, the team indeed found a design that reduced the overall noise levels at any given thrust level. Indeed, they sound more like a rushing breeze than a propeller, making a much less intrusive sound.
"The key thing that we thought was making the propellers quieter, was the fact that you're now distributing the vortices that are being generated by the propeller across the whole shape of it, instead of just at the tip," says Sebastian. "Which then makes it effectively dissipate faster in the atmosphere. That vortex doesn't propagate as far, so you're less likely to hear it."
The team analyzed these weird-looking toroidal props to see whether there would be a thrust efficiency penalty. Apparently not: the team's best-performing design was not only quieter at a given thrust level than the best standard propeller they tested, it also produced more thrust at a given power level, thereby providing a 20% fuel efficiency gain.
Pretty remarkable given that standard props have more than a century of development behind them and these toroids are at a very early stage, with plenty of optimization yet to come. Watch this space...
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