General > General Technical Chat

The Hyperloop: BUSTED

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StillTrying:
Why not leave all the air in it, but make it a very fast wind tunnel, there'd be almost no wind resistance for 'the pod' then.

T3sl4co1l:

--- Quote from: StillTrying on July 28, 2016, 02:19:57 am ---Why not leave all the air in it, but make it a very fast wind tunnel, there'd be almost no wind resistance for 'the pod' then.

--- End quote ---

Tremendous resistance from the pipe itself, and the 'pod' exhibits greater shear as the air is either confined to a smaller cross section (where the pod itself is), or the buildup of pressure waves (if supersonic flow, which would be necessary for comparable speed).

You'd need tens of atmospheres at one end of the pipe to maintain anywhere near subsonic flow, which you can imagine wouldn't go over well...  Otherwise, you'd need pumps along the pipe to maintain flow, which is just as bad.

Another way to think of it: you have less shear per unit length (maybe) on a maglev train car, which travels the same speed but through free air (not air in a pipe).  But that's drag only from the train's surface, not the entirety of the tracks it runs on!

Or in still other words:
The surface of a maglev train is only the train's body length.  The inner surface of a "pneumatic tube" is the entire length of the tube!

Tim

edavid:

--- Quote from: EEVblog on July 28, 2016, 01:48:23 am ---You can go ride it first then, good luck. I'll take the infinitely more robust and safe MagLev at half the speed thanks.

--- End quote ---

Are you sure the first ride on a 380MPH MagLev would be robust and safe  :-//

StillTrying:

--- Quote from: T3sl4co1l on July 28, 2016, 02:24:12 am ---The inner surface of a "pneumatic tube" is the entire length of the tube!

--- End quote ---
I was surprised in the simulation above, that the air wavefront didn't quickly become very bullet shaped, it didn't look right to me.

Mark_Of_Sanity:

--- Quote from: Maxlor on July 27, 2016, 12:39:10 pm ---So, the simulation is done, here's the result:



...

--- End quote ---

Can you please share your equations and calculations?
This is the second time I've seen someone mention how the cascade scenario TF points to is a miscalculaton.
Another guy I quoted earlier on mentioned that the flow would be reduced to 5% after 2km into the pipe.
I haven't seen many try and proof read thunderf00ts claim of air rushing in at full volume at the speed of sound.

Also initially you can avoid any human danger by only using this for cargo transport.

Btw EEVblog, Hyperloop is maglev train, the turbine is there to further reduce air resistance
by shoving that air under or behind the capsule apparently.


p.s.

I am also a huge fan of the maglev train and especially love the transrapid by the Germans which is now dead unfortunately.
It would attract the train on to the rail then let go, and attract 100 000 times per second to maintain a constant gap of 10mm.
What a beauty!

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