Then air coming down the other side does the same. Karmann could have given Muhamad Ali lessons. Why the formation and breaking loose is an alternating sequence is something that I would ask Mr Karmann to explain to you, only he's not here any more. I have never felt any need or desire to expend the time or energy to find out. There is a disagreeable appearance of the Karmann vortex street in downwind sailing.
Spinnakers can do it too if they are presented merely as bluff bodies.
Then they set up rhythmic swinging and then rolling of the vessel. Far better to tack downwind and get some Lift in the action, so the sails are steadying, rather than rolling agents. Now we're going in search of Lift. Every time you stroke an oar in water, or move a canoe paddle, you see a vortex, a little whirlpool spinning at the surface. That spin, or vortex, is historical evidence of an earlier forceful action between a solid and a fluid.