The phys.org article and headlines are misleading, the authors did not investigate systems to actually transmit torque. From what I gather, the interesting findings are the parameters for co-rotation and counterrotation of the driving and driven cylinder, depending on the Reynolds number, distance and so on. To illustrate one of the images of their publication: https://i.imgur.com/m8P2iVw.png

Check out what this dude came up with 120 years earlier: https://en.wikipedia.org/wiki/Hermann_F%C3%B6ttinger

I'm not a fan of the bias towards "Gears are old tech, and that makes them bad" but I can see a lot of interesting possibilities with fluid coupling. The variables involved in power transmission for these things would be pretty wild to characterize, and the article video clearly shows inefficiencies in the system with the driven cylinder having counter rotational flow against it.

Ever driven a vehicle with an automatic transmission rather than a manual gearshift with a clutch? Then you almost certainly used a fluid coupling: basically two fans in a can with oil so turning one turns the other.

The article is so full of hype it doesn't bother to explain how this is different from the "fluid gears" invented in 1905.

As what efficency? The artical doesn't say, but hydraulics and automatic transmissions have been around for a long time and are less efficient than regular gears or electric motors. Cars got a good efficieny boost then the locking torque converter was developed.

Virtually zero torque right?

Nice to see that they have discovered the Torque converter https://en.wikipedia.org/wiki/Torque_converter

Used since the 60s lol

Torque transfer through a fluid, per se, is old hat: it's been deployed in automatic transmissions starting in the 1940's. Buick's "Dynaflow", etc.

I’m super confused how this any more useful than an oil based hydrodynamic torque converter like you’d find in a “slush box” automatic transmission. The video in the article shows such a low rate of transmission it’s crazy, I can’t think of a purpose!

Do we understand fluid mechanics well enough now to just design things like this from scratch, or is it still mostly trial and error? TFA seems to imply the latter, but....

There must be some reason PRL chose to publish this, but it's not apparent to me from TFA or the abstract, and I'm not interested enough to login via my institution.

It's not new that you could set up co- or counter-rotation in such a system. This seems like the sort of thing G. I. Taylor had as a bath toy.

Maybe impossibly tiny and unresponsive torques are useful somewhere?

How is this different from slushomatics? Sounds exactly like old school fluid couplings.

Ehm, isn't it the same thing as https://en.wikipedia.org/wiki/Torque_converter ?

reminds me of a tesla turbine -- only less efficient

As immortalised in the 1978 song "Greased Ligthnin'" from the film Grease:

    Well, this car is automatic
    It's systematic
    It's hydromatic
    Why it's greased lightnin' (greased lightnin')

I am pretty sure that "hydromatic" there is actually "Hydramatic" (https://en.wikipedia.org/wiki/Hydramatic).

Many automatics these days are manual transmissions with a computer controlling the clutch. They have nothing in common with the slushboxes of old, the oil is just for lubrication.

> Ever driven a vehicle with an automatic transmission rather than a manual gearshift with a clutch? Then you almost certainly used a fluid coupling

Are you sure?

https://en.wikipedia.org/wiki/Continuously_variable_transmis...:

“The most common type of CVT uses a V-belt which runs between two variable-diameter pulleys.

[…]

A belt-driven design offers approximately 88% efficiency, which, while lower than that of a manual transmission, can be offset by enabling the engine to run at its most efficient speed regardless of the vehicle's speed.

[…]

Disadvantages of a hydrostatic CVT include:

Reduced efficiency. Gears are one of the most efficient methods of mechanical power transmission, with efficiencies as high as 90 percent in many cases. In contrast, few hydrostatic transmission systems achieve more than about 65 percent efficiency”

Except a fluid clutch actually works, and a torque converter works even better and has three fans inside it ;-)

I can see the "passive" cylinder getting dragged around a little by viscosity but I don't see how this could transfer even the tiniest amount of power.