Downwash
The video from RVDT's post has also an interesting point at around 21 min:
The speed and direction of the downwash from an observer on the ground would be more or less straight down. Wind tunnels are actually showing reality in an inverted way: it's not the air flowing around a static wing, but the wing plowing through the air. So if you picture the wing going from right to left and the air being still, you see the air is mainly deflected downwards.