# How exactly does the startup vortex form, and why does it occur when circulation around the wing changes?

So I was wondering how exactly the startup vortex forms, why it dissipates, and where it's located in relation to the trailing edge of the wing. Also, why does a startup vortex form when circulation around the wing changes? (see quote below)

"This starting vortex formation occurs not only when a wing is first set into motion, but also when the circulation around the wing is subsequently changed for any reason whatever." Millikan, Clark B., Aerodynamics of the Airplane

If someone could explain that to me, I'd appreciate it, thanks

(If someone could also explain how the tip vortices contribute to the startup vortex, I’d also appreciate it)

(What I meant by startup vortex ^)

• It's written just a couple of line before in the same book. I'd also suggest you to use something more modern 😉 Commented Nov 14, 2023 at 7:06
• Maybe this answer or this one help? Commented Nov 14, 2023 at 19:21
• @sophit thanks, those answers did help a bit, but I'm still kind of stuck on why exactly the vortices stop being formed when at higher speeds, and why changing circulation will make startup vortices. I read the lines in the textbook you provided but I am still a bit confused. Commented Nov 14, 2023 at 21:16
• It's just a matter of Newton's second and third law (aka momentum conservation). If the circulation around the airfoil changes (in time or space) then a proportional and opposite circulation is released in the wake. Commented Nov 15, 2023 at 5:42
• @sophit Ah okay, so what direction and where will the startup vortex formed from changing circulation be? Commented Nov 15, 2023 at 21:38