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-   -   Which direction is positive direction in moment coeffs? (https://www.cfd-online.com/Forums/openfoam-post-processing/115679-direction-positive-direction-moment-coeffs.html)

wes1204 April 4, 2013 14:35

Which direction is positive direction in moment coeffs?
 
hello everyone.

I obtained Cd, Cl, Cm using execFlowFunctionObjects.

------------------------------------------------------------------------------------------
forcesCoeffs
{
type forceCoeffs;
functionObjectLibs ( "libforces.so" ); // lib to load
outputControl timeStep;
outputInterval 1;
patches
(
wall // change to your patch name
);
// name of fields
pName p;
UName U;
log true; // dump to file
rhoName rhoInf;
rhoInf 1.25;
CofR ( 2.3 0.7569 0 );
liftDir ( 0 1 0 );
dragDir ( 1 0 0 );
pitchAxis ( 0 0 1 );
magUInf 1.43;
lRef 0.3537;
Aref 0.3537;

-----------------------------------------------------------------
my case is something like airfoil.

I set pitchAxis( 0 0 1 ).
in this case, which direction is positive in Cm??
clockwise? or countclockwise?

please help me

wes1204 April 8, 2013 08:26

help me...
 
anybody help me...

Tjcross31 May 21, 2021 22:56

Hi wes,
I know this is years later but this same issue of sign conventions came up in my Masters' project recently - I'm posting here in case anyone should also come across it.
Quote:

Originally Posted by gfoam (Post 342824)
The moment coefficient in libforces.so, is possitive under the rule of the right hand, while in aeronautics, the pitching moment is possitive nose up. I think this may the cause of your differences.
Gonzalo



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