Am 05.02.2016 um 06:49 schrieb Sven Littkowski:

> Now let me answer your question. The cylinder rotates, and its inner
> sides contain objects, such as buildings, moving objects (like humans
> and vehicles, maybe even animals), and also trees and other plants.
> Those all will "push" the air and get thus the air into motion. Over
> time, the air at around all these objects will gain almost the same
> speed as the inner walls of the cylinder and the objects on it.
> 
> But since air is flexible, the air at the outer areas moves initially
> faster than the air along the central middle axis of the cylinder, but
> over time, that air there tends to gain speed, too, pushed by the air
> from the outer areas.
> 
> However, since air has its own inertia, the air especially at the inside
> will never reach a full 100% of the air movement close to the walls of
> the cylinder.

You may be pretty much mistaken there.

First, let's look at what would happen /without/ any external influence.
If we do not input any energy, the system will approach equilibrium,
which would be characterized by the following conditions:

- All portions of the system will have the same temperature. As a
consequence, there will be no temperature-induced air movement.

- There will be no friction between the air and the ground, as any such
friction would transfer energy between the two, and therefore constitute
an indication that equilibrium has not yet been met. Note that absence
of friction between air and ground can only be achieved by having the
air rotate at the same speed as any ground structures at the same heigth.

- There will be no turbulences within the air, as any such turbulences
would transfer energy around within the body of air, and therefore again
constitute an indication that equilibrium has not yet been met. Note
that the absence of turbulences can only be achieved if the air moves
like a solid body would.

=> Without external energy input, the angular velocity will become
uniform across the entire system.


Now let's see what happens if we add a sustained heat source:

- If we heat up the air near the central axis, nothing much will happen:
Warmer air tends to travel inward, so we don't get any convection. We
would get some slow heat transfer outward, and a change in the pressure
gradient, but no noticeable movement.

- If on the other hand we heat up the air near the ground, that warmer
air will indeed, through convection, exchange its place with the cooler
air near the axis. However, as both layers of air initially have the
same angular velocity but different distance to the center, they have
different angular momentum, which needs to be conserved. The only two
mechanisms by which this can be achieved is (a) by transfer of angular
momentum from the warm air moving inward to the cold air moving outward
by means of friction (which is inefficient), or (b) by a change of
angular velocity in the respective bodies of air.

As a consequence, the warm inward-moving air will increase its angular
velocity beyond that of the ground, while the cold outward-moving air
will decrease its angular velocity below that of the ground, initially
resulting in a net wind at ground level.

- If the heat input continues, the convection will also continue, and
turbulences in the air will not subside; however, the net wind at ground
level will lead to a transfer of rotational energy between ground and
air until both ground and ground-level air generally move at the same
speed. Note that this effectively speeds up the ground-level air (while
slowing down the ground).

- The mechanism by which higher-level air is sped up, however, does
/not/ subside; to the contrary: With the ground-level air speeding up,
the difference in speed gets even more pronounced.


=> From what I see, we should expect the air near the ground to be
motionless overall, with winds only blowing from cooler ground regions
to warmer ones, while closer to the center we should expect a /higher/
angular air velocity than near the ground.

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