Is circulation real?

I always demonstrated circulation as part of my class on propellers. You can take an aluminum turkey pan, fill it with water, sprinkle pepper on the water, then using a spatula or a butter knife as a foil put it in the water on one side, draw it across the water at an angle of attack then quickly lift it vertically out when you get to the other side of the pan. If your angle of attack wasn't too large you will see the starting vortex and the bound vortex just as shown in the sketches above.

If the pan is deep enough and you wait until the first shake of pepper gets saturated and neutrally buoyant, you can sometimes see the trailing vortex along the bottom of the pan as well.

As to the sailing thought experiment, this is a trick seagulls routinely use. They ride the upside of the sail's training vortex to save having to flap. I had frequently had such company crossing the SF Bay. They could go all the way from Sausalito to Gas House cove without moving their wings.

 

Michael Dickinson at CalTech has been researching insect flight since the early 1990's. His research has included high-speed photography and instrumenting of insects, building custom fluid tunnels to model insect flight, and computer simulations. MacArthur Fellow and smarter than most, he shows pretty clearly that aerodynmaci circulation is 'real.' Check out this introductory video on YouTube:

Michael Dickinson (CalTech) 1: How Flies Fly: Lift