# When two opposing vortexes combine to form a dipole vortex, why does it always move in the same direction?

AS you know, when two opposing vortexes combine to form a dipole vortex, it always move in the same direction as shown with red arrow in figure below. I wonder, why? is there a equation for this motion?

• Do you have an example of this phenomenon happening? I have seen this when the eddies are produced by the two edges of an oar blade, but in that case the purpose of the oar blade was to cause bulk motion of the water.
– rob
Nov 12, 2022 at 14:49
• yes many have. if one vortex of dipole is bigger than the other, smaller vortex turns around bigger vortex. if two vortex are equal, they move in the direction of inner flows between them. look at all these videos; youtube.com/watch?v=UxlSCe111IA youtube.com/watch?v=rpcqI11d3gc youtube.com/watch?v=QP6ngTP8W80 youtu.be/rF3phfLv7QM?t=12 Nov 12, 2022 at 16:03
• @HakanEgne it's simple to understand why just by considering the flow induced by one vortex at the position of the other vortex core. See this answer: physics.stackexchange.com/a/663790/226902 May 17 at 7:56