The Secret of Separation

The Secret of Flight revealed in previous posts is hidden in the secret of separation of the flow at the trailing edge of a wing. The above picture reveals the Secret of Separation:

You see a piece of the trailing edge of a horisontal wing as viewed from behind with opposing (more or less) vertical flows from the upper and lower side of the wing which are meeting in retardation and somehow have to be directed into a (more or less) horisontal backward direction to leave the wing (out of the screen). You can think of two opposing armies approaching each other and the question is how the conflict is to be resolved.

Now, retardation in opposing flows is exponentially unstable (direct confrontation is unstable) and thus the flow seeks a flow pattern without opposing flow, and finds one as depicted above: The opposing flows are shifted horsiontally and turned into a set of counter-rotating swirling vortical motions like the one you can see in a bathtub drain, as seen here in a different perspective.

The result is a separation without unstable opposing flows supported by a zig-zag pattern of low/high pressure with low pressure inside the vortices, as shown here. The resulting pressure distribution is what gives both drag and lift to a wing.

Something to think about in the hammock, or in your sailing boat because the secret of sailing is the same.