Particles floating inside a volume

[Fabrice]

- Adding a +1 gravity to the force : I did that to compensate the -1 gravity that PhysX shape adds automaticaly (and...I couldnt find where to turn it off in the PhysX Shape parameters).

When you grab TyFlow object in the scene (the same one you created when you created TyFlow), if you go to modify panel, under PhysX rollout you can see that gravity and ground collider are enabled by default. You can disable them there. 
---------------------

Is something like this that you want? 
(attachment)

Sorry I didnt answer!

I dont think the physX worksbecause it makes particules bounce against the volume's limits.
So the movement wont be smooth as should be dust or birds flying.

I dont see any solution.
Using a find target and playing with velocity + acceleration allways ends up with something very fast and noisy, 
or someting that wont respect the shape of the volume
even with a strong slow operator.
I couldnt find a good solution...