Active Drag Reduction?

I used to walk past this boat most weekends:





It has gone from the Maritime museum now

 

Nice toy, but real issues. There are some things in engineering that just don't scale. Also that first "flight" looked a lot like Langley's first flight claim.
For issues with ion for marine propulsion, see this discussion.
Anyone played around with a magnetohydrodynamic drive? https://www.boatdesign.net/threads/anyone-played-around-with-a-magnetohydrodynamic-drive.44464/
If I recall from articles on Yamato 1, they were spending more energy on making the liquid Helium than it would have taken to power her faster with a conventional propulsion system. Like with anything it is horses for courses, ion engines work great in space where at tiny bit of force over a very long time is meaningful.

 

My suggestion isn't to use this technology as a drive, but instead to use it for active drag reduction. Where speed is the number one issue, energy efficiency isn't a consideration. No liquid helium necessary.

I haven't been able to wrap my head around this technology as a space drive. It seems to me, it needs a conductive medium to operate in. Where do the electrons come from in space?

 

They are stripped off a source...remember how old tube amps and CRT's worked?
Edit: I may have misinterpreted you question....There are many small particles in space; dust, gases, and the "solar wind": basically all the high energy particles (H and He nucelli, free electrons, protrons, and neutrons, etc.) that escape the sun without hitting or getting captured by something.

 

The problem with these setups is they need an active air feed and a specialized morphology plus the holes which shoot air will get clogged with fouling and stop working after one month, this may work for racing boats where you haul them out of seawater for the off-season. I think there aren't any manufacturers making air-cushioned hulls by the way. There are various films that come out from time to time, these never really work plus there's the hassle of adhering and keeping it adhered to the hull, the last film which got funded btw is https://aircoat.eu/ , there was another film sharkskin that came out decades ago and worked the same way but the 10% drag reduction didn't cut the lack of fouling resistance.

Regarding using MHD for drag reduction yes it's possible but will you fund it? It is probably even more uncommercializable than the films they try to sell from time to time.

 

-Will

 

ok what do hovercrafts have to do with drag reduction for boats?

and you want to make mhd drag reduction for what purpose? even if you shoot water downwards it doesn't necessarily mean this will automatically create an air cushion

superhydrophobic surfaces don't work either when there's a large pressure exerted on them otherwise everyone would just coat boats with SH coatings

in theory you can exert a downward pressure in the incoming water with EM forces but you have to minimize EM drag because this would cost you propulsive energy in the exchange for an upward force and if the surface is not suitable no air cushion will be created , there are a few papers about this... just do a google search, as I guessed no one has made one that works energy wise

1970 navy paper

Torpedo Drag Reduction Using Magnetohydrodynamic Boundary-Layer Control. https://apps.dtic.mil/sti/citations/AD0735471

 

These thoughts are NOT expressions of desires, but ideas for exploration and discussion.

Do you seriously not see the connection between hovercraft and creating air cushion drag reductive layers?

 

it's too different, the hovercraft skirt is only in contact with seawater during operation and stored on land, the rubber which they use is probably butyl rubber or similar, they use huge blowers which allows them to use a flat surface

about the MHD drag reduction if it was easy it would already have been implemented

you can either ionize the water molecules with electret materials or capacitors and pass them through permanent magnet fields or you can create inductive currents or create magnetic fields with coils, the problem with the last two is with induction and coils you waste energy to heat because you will probably not use superconductors, if you use superconductors you waste energy to cool them in order not to waste it in heat, if you use permanents magnets you cannot control the magnetic fields enough so you will create eddy currents which will induce an opposing force to the motion of the vessel
you can think of this as similar to coil guns or rail guns, huge amounts invested and still nothing usable as of yet

still even if you make it the force will be on the water so you will push the water downwards and the vessel upwards, this doesn't change the inertia of the vessel, it effectively lifts it up, it's not sure it will create an air cushion unless you use specialized geometry

 

Do you know about surface wetting? There are surfaces that like certain liquids such as water and materials that don't like them, when a surface likes a liquid it attracts it, there are many electrostatic forces like dipole-dipole e.t.c. called van der waals forces that are more prevalent in hydrophilic than hydrophobic surfaces in contact with water, the problem is that even if you make a hydrophobic surface it cannot overcome the rise in pressure when the vessel is moving or when it is submerged over some meters because surface wetting depends on pressure. If you make an MHD metamaterial you can modify the surface wetting at all pressures and thus modify the boundary layer of this surface with water.

oof found 1 research about this but they focus on laminar flows instead

https://www.researchgate.net/public...with_active_magnetohydrodynamic_metamaterials

 

We design and help to construct hovercraft and surface effect ships...have for 35 years. We were also involved in a number of surface drag reduction projects, using air as well as polymer "juice" injection in to the boundary layer.. There is nothing in common between the two methods. None of the surface drag reduction projects resulted in a reduction of drag when attempted on a larger demonstration craft.

 

What was the difference in the air moving system for injection of air into the boundary layer compared to the air moving system that creates the cushion of air that a hover craft rides on?

I just have my imagination to work with here, but I'm imagining the only real difference is in the hull shape and the manifold delivery nozzles.

 

They do both require prime movers and lift fans or some other sort of compressor to supply pressurized air. The ACV and SES fully capture the air in a compressed bubble that provides static lift of the vessel between 80% (SES) and 100% (ACV) of the total displacement..even at zero speed. .