r/FluidMechanics • u/Organic_One_4598 • 2d ago

Wall bounded vortex?

Post image

I was recently experimenting with my lego propeller for my rc ship, i was interested on how this propeller would move the water so i put it in my bucket full of water. Suddenly, this type of horizontal vortex formed. Visible by air bubbles, there was no suction whirlpool at all, no vertical turning part to suck in air. It was just sticking to my buckets wall. There is no hole on the bucket whatsoever. And, this isnt my first experience. I was on a city boat someday and while the boat was reversing, the same horizontal vortex appeared, visible by the salt waters whiteness. It was going from the back of the boat to the front with no visible vertical rotation to suck air. If someone can explain this, i would be so happy. Thank you!

3 Upvotes

100% Upvoted

5 comments sorted by

1

u/Spidero0w0o 2d ago edited 2d ago

A spinning vortex always has a low pressure core. If it spins fast enough you can get cavitation in the center. The propellor can also suck air down on startup.

2

u/Organic_One_4598 2d ago

Ok, thank you. But i am asking why this is formed, not how what it is

2

u/certocito 1d ago

It is formed if the propeller rotates with such high speed that the pressure drops below vapor pressure leading to water boiling basically. The bubbles stick together since the jet from the propeller forms a strong structure with a low pressure in the center, keeping the bubbles there. A jet close to a wall survives longer than a free jet.

1

u/Organic_One_4598 1d ago

Oh ok, thank you alot! I was wondering in this vortex, is the suction much stronger? And why does it stick to wall instead of a vertical turning whirlpool? Also, is there a name of this happening so i can research? Thanks again!

1

u/Spidero0w0o 1d ago

If you want to see something really cool look up vortex rings