Fluid dynamics in rotating rigid container

[michaelwoodcoc]

Pascal's law seems contradictory to what I would expect. If the pressure in a hydraulic system is equal everywhere, but you have a fluid, completely filling a rotating cylinder, wouldn't the force on the walls be greater than the fluid pressure in the middle due to the centripital forces?

Can one apply a negative pressure to the fluid to decrease the forces?

Engineering student. Electrical or mechanical, I can't decide!
Minoring in psychology

 

[hydtools]

Pascal's law states that the change in pressure to a confined liquid will transmitted equally. Look at the pressure distribution in a vertical column of water due to the force of gravity. Push on the top to create a pressure change and the pressure at the bottom changes by that same amount. Imagine the column in the dirction of the centrifugal force. There will be a pressure distribution from the center outward. Push on the outer confining surface and the pressure change will transmit equally throughout the fluid, per Pascal's Law.

Ted

 

[btrueblood]

1. Yes
2. No, there is no such thing as "negative pressure". You could reduce the pressure to zero (pull a vacuum) at the centerline, but can't go below zero. You could also reduce the stress on the cylinder by increasing the external pressure. Or just make the wall thicker...

 

[3DDave]

https://en.wikipedia.org/wiki/Pascal's_law

Any law, incompletely stated or applied outside its confines, will appear to have contradictions.

 

[electricpete]

I think the key assumption for Pascal's law is a hydrostatic condition (there is no fluid flow).

The rotating cylinder is dragging some of the outer fluid around with it causing some circulation. So you're not meeting that hydrostatic condition.

=====================================
(2B)+(2B)' ?

 

[hydtools]

What if the axis of rotation is perpendicular to the cylinder axis? No drag friction, no circulation.

Ted

 

[rb1957]

I'd've thought that the fluid inside any rotating tank was not at rest nor at the same pressure

another day in paradise, or is paradise one day closer ?

 

[GregLocock]

Shouldn't have deleted my earlier answer

A change in pressure at any point in an enclosed fluid at rest is transmitted undiminished to all points in the fluid.

Pressure exerted on a fluid in an enclosed container is transmitted equally and undiminished to all parts of the container and acts at right angle to the enclosing walls.



Cheers

Greg Locock


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