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# Fluid dynamics in rotating rigid container

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## Fluid dynamics in rotating rigid container

(OP)
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

### RE: Fluid dynamics in rotating rigid container

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

### RE: Fluid dynamics in rotating rigid container

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...

### RE: Fluid dynamics in rotating rigid container

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)' ?

### RE: Fluid dynamics in rotating rigid container

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

Ted

### RE: Fluid dynamics in rotating rigid container

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 ?

### RE: Fluid dynamics in rotating rigid container

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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