When watching the images or movies that show the rotating tank from the outside, you may have been wondering about why the whole structure — tank, office above the tank, everything — is inside a rotating tent, which itself is inside a large room.
Remember the last time you were on a merry-go-round? Remember the wind on your face and in your hair? Yes, that’s exactly what we don’t want. Neither for us sitting in the office, nor, more importantly, for our tank.
If there wasn’t a tent around the whole structure, rotating with it, we would always have “wind” on the tank’s free water surface, because the water would be in motion relative to the room in which the tank is located. The friction between air and water would then cause wind-driven surface currents, which might disturb our experiments. Now, however, the air inside the tent is rotating with the tank, hence there is no motion of the air relative to the water, no wind, no wind-driven currents, perfect conditions for our experiments!
And believe me, when you step out of the tent on your way off the rotating platform, or from the stationary room onto the platform on your way in, you definitely feel the wind!