## Subtitles section Play video

• [Engines screaming]

• Hey it's me, Destin. We're at an airshow.

• So today I'm going to teach you about vortex shedding.

• [Music]

• [Engines screaming]

• (Man) YEAH!

• (Destin) Fly... flying our airplanes.

• [Engine roaring]

• (Destin) I can't hear you. Why does the smoke come out of the airplane?

• (Sadie) To help it go better.

• - Makes perfect sense.

• [Engine roaring]

• [Propellers thumping]

• So on a wing...

• You know, in layman's terms, the Bernoulli principle -

• where flow is high, pressure's low. Got it?

• Where flow is high, pressure's low.

• So the air has to travel farther over the top of the wing than on the bottom,

• so it's flowing faster. So we have low pressure on top

• and high pressure on the bottom.

• So high pressure pushes the airplane up. That's why the airplane flies.

• But something you didn't know:

• if you're on the edge here... if you look at this,

• we've got high pressure and low pressure

• and they try to have a discontinuity here,

• So what happens is that high pressure tries to run around the top of the aircraft,

• and you get what's called a vortex, or vortex shedding.

• And you can calculate the vorticity on that.

• So let's go to the other axis.

• Okay, so now we're looking at the tip of the wing.

• So again, you have low pressure on top, high pressure on bottom.

• So that high pressure runs around...

• The flow runs around and tries to roll over so that they can meet,

• because nature abhors a vacuum; it doesn't like discontinuity.

• So what happens is, as it rolls you get a vortex in this direction here.

• [Engine roars]

• Okay, you can see on this wing what they've got on the end

• is it's kicked up just a little bit.

• So you've got the high pressure here flowing around,

• and you've got the low pressure here, but it's also swept.

• If you come around at this angle and look,

• you can see that it's swept, and the whole idea is to control the vortices

• as they shed off the end of the vehicle. So that's it.

• You reduce drag by getting that off of the vehicle

• and getting it out and away from you.

• [Birds chirping]

• Can you say hello? - Hewow.

• It's me and my buddy, and we're on a kayak,

• and we're overlooking a hot air balloon festival.

• Okay, vortex shedding does not only happen with airplane wings,

• it also happens with things like paddles.

• If you have a low pressure and a high pressure side on the paddle,

• You get the discontinuity right on the edge

• [Destin laughs]

• I'm really ruining my canoe trip with my buddies. [Laughs]

• Anyway, you get vortex shedding and discontinuity on the side, so watch.

• When you watch the paddle here, you'll see a vortex occur right on the edge.

• You'll notice it happens where it's rolling from the high pressure side

• to the low pressure side.

• (Child) Could you see the flames? (Other child) Yeah!

• (Destin) I'm going to show you an example of

• what life is like without asking science questions of yourself all the time.

• So, Jacob, my friend,

• why do you say that there's a vortex on the edge of the wing on a fighter jet?

• (Jacob) Because... - No, you gotta look a the camera!

• - Oh! It's the camera.

• Because Tom Cruise was cool in Top Gun when he was the Maverick.

• That's before he went crazy and needed to go do the loops.

• - It has been noted.

• If you don't ask scientific questions of yourself

• you'll go through life thinking Tom Cruise is cool.

• [Destin laughs]

• (Destin) What's this called? (Jacob) Vortex shedding.

• - How did you know that? - Because I have smart friends.

• - Whatever.

• (Woman) We have a rocket scientist... (Jacob) I know a rocket scientist.

• (Destin) A-10 Warthog. That's where it's at.

• [Engine screaming]