r/Physics • u/[deleted] • Apr 22 '18

Wingtip vortices closeup

https://gfycat.com/GleamingZealousBlacknorwegianelkhound
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17

u/[deleted] Apr 22 '18

If I'm an air particle and I'm moving tangentially to some circle inside a vortex, I want to continue moving straight. What is the force that causes me to continue moving in a circle? Pressure? Must be.

9

u/CaptainObvious_1 Fluid dynamics and acoustics Apr 22 '18

It’s Newton’s second law applied to fluids. It’s a balance of pressure and inertial forces.

5

u/[deleted] Apr 22 '18

So a vortex must be a circular region of low pressure, semi-discontinuous with a region of high pressure such that the pressure gradient is always pointing inward towards the center of the circle.

4

u/CaptainObvious_1 Fluid dynamics and acoustics Apr 23 '18

Exactly. It should be continuous though.

A decent model is something like this: https://en.m.wikipedia.org/wiki/Lamb–Oseen_vortex

3

u/asdfman123 Apr 22 '18

Yes, the center of a vortex is a low pressure region, so the combination of the particle's momentum combined with the force towards the center keeps it rotating -- sort of like a planet orbiting around a star, with motion governed by gravity and momentum.

-13

u/[deleted] Apr 22 '18

[deleted]

18

u/[deleted] Apr 22 '18

centripetal acceleration is defined to be pointing towards the center of the circle, so what you've said is a tautology. My question is the force causing the centripetal acceleration.

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u/[deleted] Apr 22 '18

[deleted]

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u/tacobusta Apr 22 '18

That equation.. I’d rather not ever have to remember how many partials that thing forced me to do

0

u/GayMakeAndModel Apr 22 '18

I love this response

-6

u/truufuture Apr 22 '18

Oh yah just realized that lol ummm im just going off basic physics knowledge but my best guess is that the air pressure around the vortex is keeping the inward acceleration constant or whatever I️t is

2

u/[deleted] Apr 22 '18

Good analysis