Halbach array fans for aeropropulsion

ladajo · Post by **ladajo** » Thu Aug 05, 2010 12:36 am

KITE: Yes he worked on the composites, and the issue they were having was the magnetically excitable material would unbond from the composite flywheel, and make for some catastrophic (cool) fails.
The concern was that the use of the flywheels in consumer applications could bring high risk if the entire device had a short term full energy release. Ie: we canna make the dilithium box stronganuff for the dilithium blast...
I am dredging from 14 year ago memories talking it over with him.
They had a good grip on magnetic bearings, and the concept, but the physical makeup of the rotor was apparently the issue as they could not find a method at the time to reconcile the differnce in densities in the composite disk to the magnetic inserts, and at high rotor speeds this put incredible stresses on the rotors to the point of failure.

DeltaV · Post by **DeltaV** » Thu Aug 05, 2010 1:32 am

ladajo wrote:KITE: Yes he worked on the composites, and the issue they were having was the magnetically excitable material would unbond from the composite flywheel, and make for some catastrophic (cool) fails.
The concern was that the use of the flywheels in consumer applications could bring high risk if the entire device had a short term full energy release. Ie: we canna make the dilithium box stronganuff for the dilithium blast...
I am dredging from 14 year ago memories talking it over with him.
They had a good grip on magnetic bearings, and the concept, but the physical makeup of the rotor was apparently the issue as they could not find a method at the time to reconcile the differnce in densities in the composite disk to the magnetic inserts, and at high rotor speeds this put incredible stresses on the rotors to the point of failure.

I can see that being an issue for flywheel storage at 10000-20000 or more rpm. The Livermore design I mentioned got around that, IIRC, by spinning lightweight Litz wire embedded in the rotor, instead of the heavy, cylindrical Halbach array which surrounded it. Halbach for a uniform B field, not necessarily as bearings, but it did have magnetic bearings too, I think. Saw this ten years ago, so I'm fuzzy on the details, might have it backwards.

NASA's Halbach-levitated, ducted fan has a design speed 0f 6630 rpm, so maybe the perm magnets don't separate from the composite at that lower rpm.

rjaypeters · Post by **rjaypeters** » Fri Sep 03, 2010 4:37 pm

This may be off topic, but is conceptually related.

Looking back at the origin of this thread:

DeltaV wrote: http://gltrs.grc.nasa.gov/reports/2006/ ... 214481.pdf

Motors in the rim reminds me of boat thruster designs which have gone hubless.

http://www.boatdesign.net/forums/propul ... 432-4.html

Looks like they are planning on main propulsion units also.

ladajo · Post by **ladajo** » Fri Sep 03, 2010 9:03 pm

Nifty adaptation to a been around long time concept, "canned rotors".

Only one thing better, electrohydrodynamic motors. Just need a good size power source...hmmm...oh, Polywell!

DeltaV · Post by **DeltaV** » Fri Sep 03, 2010 11:52 pm

Low speed, high thrust for large diameters ("lift fan"). High speed, lower thrust for smaller diameters, several cascaded along a duct ("turbine"). High temp superconductors, a la Prins.

The one pictured is for boat thrusters in water, of course, not air. Different blade shapes and materials for air, and Halbach magnetic bearings.

For the air turbine, with several stages inline, imagine each stage's rpm controlled independently to optimize overall thrust/efficiency at any flight condition.

DeltaV · Post by **DeltaV** » Mon Sep 13, 2010 7:56 am

Another passive (no power supply or control circuits/actuators needed) electromagnetic bearing, an alternative to Halbach arrays for smaller diameters. Lower eddy current losses:
http://en.wikipedia.org/wiki/Electrodynamic_bearing
Good also for very high speeds, e.g. turbomolecular pumps.

GIThruster · Post by **GIThruster** » Mon Sep 13, 2010 2:27 pm

I'm not a materials specialist but what little In k now suggests the ideal material for these is liquid metal. It can be injection molded for fantastic uniformity between blades and the process is cheap enough that it's being used for things like skiis and snowboards. It's not a high temperature application, but none of these blades, for air or water; are going to get very hot.

http://www.liquidmetal.com/applications/

chrismb · Post by **chrismb** » Mon Sep 13, 2010 7:00 pm

GIThruster · Post by **GIThruster** » Mon Sep 13, 2010 7:22 pm

DeltaV wrote:Low speed, high thrust for large diameters ("lift fan"). High speed, lower thrust for smaller diameters, several cascaded along a duct ("turbine"). High temp superconductors, a la Prins.

The one pictured is for boat thrusters in water, of course, not air. Different blade shapes and materials for air, and Halbach magnetic bearings.

For the air turbine, with several stages inline, imagine each stage's rpm controlled independently to optimize overall thrust/efficiency at any flight condition.

Fascinating that the blades don't extend to the center of the duct. I wonder if this is to avoid cavitation? Why would it be more efficient to not fan the center of the fan in water?

I once knew a Navy machinist who used to brag that he knew what the props looked like on our fast-tack subs. He said they were classified because their special design avoided cavitation and so were especially quiet. Well, avoiding cavitation does more than make it quiet, I'd wager. There's a lot of wasted energy in creating vacuum (as well as that noisy "pop" when the vacuum collapses.

chrismb · Post by **chrismb** » Mon Sep 13, 2010 8:16 pm

MSimon · Post by **MSimon** » Mon Sep 13, 2010 8:27 pm

Why would it be more efficient to not fan the center of the fan in water?

I'm just guessing here:

1. The added thrust from the center is not significant. The turbulence from the hub doesn't help.

2. The inertia of the fluid column is better handled by a hole than a hub.

ladajo · Post by **ladajo** » Mon Sep 13, 2010 11:00 pm

I would say turbulence control.

And if you want to see what a submarine propellor looks like, google it.

http://www.bing.com/maps/default.aspx?v ... &encType=1

And thanks to our friends at Toshiba...cavitation noise became less of a problem for soviet (& chinese) boats...

But something happened to change all that. Back in the mid-1980s, the Japanese company Toshiba sold propeller milling machinery to the Soviets through the Norwegian Kongsberg firm; this and other submarine intelligence furnished by the Walker spy ring resulted in significantly quieter Soviet subs by the later part of the decade. As writer Neal Stevens wrote about the Akula-class Soviet boats, "The combined results generated a steep drop in broadband acoustic noise profiles."

GIThruster · Post by **GIThruster** » Mon Sep 13, 2010 11:01 pm

ladajo wrote:I would say turbulence control.

And if you want to see what a submarine propellor looks like, google it.

http://www.bing.com/maps/default.aspx?v ... &encType=1

Yes, same as in Red October. Not such a secret after all.

DeltaV · Post by **DeltaV** » Tue Sep 14, 2010 3:51 am

How did this thread get moved from Design to the "Pot and Politics" forum, to be rapidly buried and forever hidden from the purview of DIY Polywell space hopper buffs?

Ahh... the deleted chrismb posts... not Polywell design related, eh? Maybe he works for Reaction Engines, Ltd.?

I'd rather it had been moved to Implications instead of (ugh) General.

DeltaV · Post by **DeltaV** » Tue Sep 14, 2010 4:06 am

MSimon wrote:
Why would it be more efficient to not fan the center of the fan in water?

I'm just guessing here:

1. The added thrust from the center is not significant. The turbulence from the hub doesn't help.

2. The inertia of the fluid column is better handled by a hole than a hub.

Sounds about right. One drawback is that the blades have to be more resistant to compressive buckling, not that big of a deal with the right material.

Talk-Polywell.org

Halbach array fans for aeropropulsion

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