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-   -   Force reports: calculation comprises face areas? (http://www.cfd-online.com/Forums/fluent/111481-force-reports-calculation-comprises-face-areas.html)

Zelle January 8, 2013 09:05

Force reports: calculation comprises face areas?
 
Hi everyone,

if I let FLUENT calculate total forces that act onto a wall using "Force reports", will the calculation procedure comprise the face areas?
I read the theory guide, but didn't get it :confused:.

My problem is, this 3D-wall is meshed by different sized faces. So I will have to inlcude each face area to calculate a total force.

Marion January 8, 2013 10:09

Hi Zelle,

You have to specify the wall where you want the force to be calculated as a specific boundary condition. For example, when I compute the force on the ball of a ball valve, I create a wall BC in the meshing tool (Gambit or Design modeler) called "ball", to separate this fromt he rest of the walls in my model.

Marion.

Zelle January 8, 2013 10:22

Hi Marion,

this (my) 3D-wall has a spherical shape and is already treated with a wall boundary condition. If I get the theory guide right, FLUENT only sums up the forces that are acting onto each face area. This means, the total force on the wall strongly depends on the face area size distribution across the wall surface. Do you agree?

Thank you!

Marion January 9, 2013 02:50

Hi,

Are you talking about the size of your mesh elements?

If so, then the force does not depend on the size of the cell faces: the force calculations is made by summing up the forces on each cell face that is part of your wall.
the force is pressure * area, therefore the total force is
F=sum(Pi*Ai), it does not depend on the area of each mesh because if you separate a wall in 4 parts, the total area will still be the right one.

I hope this helps, it's not easy to explain writing it!

Marion.

Zelle January 9, 2013 04:28

Hi Marion,

thank you very much! You are right. I made a mistake by not thinking of the pressure...

Cheers,

Zelle


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