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November 11, 2009, 08:10 |
Forces and drag coeffs in simpleFoam
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#1 |
New Member
Milos Stanic
Join Date: Mar 2009
Location: Novi Sad, Serbia
Posts: 29
Rep Power: 17 |
Dear FOAM-ers,
I've searched through the forum and I couldn't find an appropriate answer to some basic things on how to obtain forces and/or drag coefficients in simpleFoam solver. As far as I've seen, people usually used forceCoeffs functions, but I was unable to modify them in order to work in simpleFoam. Please, if anyone has some tutorial-like instructions, I would seriously appreciate it. Thanks! Milos |
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December 15, 2009, 09:19 |
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#2 |
New Member
Kai-Jia Han
Join Date: Nov 2009
Posts: 4
Rep Power: 16 |
functions
( forces { type forces; functionObjectLibs ("libforces.so"); patches (PARALELL); rhoInf 1000.0; CofR (0 0 0); } ); |
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December 15, 2009, 09:21 |
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#3 |
New Member
Kai-Jia Han
Join Date: Nov 2009
Posts: 4
Rep Power: 16 |
I am running turbFoam for a series 60 hull and outputting viscous drags. My question is what is the unit in forces.dat? Are they in unit of Newton (both pressure forces and viscous forces)?
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December 16, 2009, 04:06 |
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#4 |
New Member
Milos Stanic
Join Date: Mar 2009
Location: Novi Sad, Serbia
Posts: 29
Rep Power: 17 |
That was my question as well... I get some huge numbers for the forces and I am not sure whether it's Newtons or sth else.
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December 16, 2009, 04:32 |
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#5 |
Senior Member
Anonymous
Join Date: Mar 2009
Posts: 110
Rep Power: 17 |
If you set rhoInf = 1, Area = 1, and velocity = 1, then I believe libforces.so will give you the 2*Force in Newtons as it is integrating the pressure and, I believe, the shear stresses on the surface (the 2 comes from the half in the dynamic head). If in doubt, compute the forces in ParaView and compare them to Foam.
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December 16, 2009, 04:35 |
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#6 |
New Member
Milos Stanic
Join Date: Mar 2009
Location: Novi Sad, Serbia
Posts: 29
Rep Power: 17 |
I didn't know that there was a way to compute forces in ParaView... How do you do that?
Thanks! |
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December 16, 2009, 09:46 |
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#7 |
New Member
Kai-Jia Han
Join Date: Nov 2009
Posts: 4
Rep Power: 16 |
Till Milos: http://www.cfd-online.com/Forums/ope...rces-of15.html
This page might be helpful for you. |
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December 16, 2009, 09:49 |
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#8 | |
New Member
Kai-Jia Han
Join Date: Nov 2009
Posts: 4
Rep Power: 16 |
Quote:
However, for force output, are the viscous forces in Newton? Or are they in fact calculated by (real viscous force)/ rho? The other question is related with symmetry. If I have symmetry patch defined in boudanry condition (for example, I only calculate half of this ship), then should I manually multiple 2 for the forces I get from forces.dat? Thank you for any suggestions and comments in advance! |
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