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-   -   forces: What are magUInf, lRef, Aref? (https://www.cfd-online.com/Forums/openfoam/85764-forces-what-maguinf-lref-aref.html)

 klausb March 6, 2011 16:07

forces: What are magUInf, lRef, Aref?

Hello,

I want to optimise a wing, hence analyse cl/cd using the forces function but I don't know the meaning of some variables (magUInf, lRef, Aref).

Actually my wing is a hydrofoil therefore the high rhoInf = 1000 kg/m3 for water.

Her the "draft" entries in my controlDict:

functions
(
forces
{
type forces;
patches (stlSurface); // change to your patch name
rhoInf 1000; //Reference density for fluid
rhoName rhoInf;
CofR (0.15 0 0); //Origin for moment calculations
outputControl outputTime;
}
forceCoeffs
{
type forceCoeffs;
functionObjectLibs ("libforces.so");
patches (stlSurface); //change to your patch name
rhoInf 1000;
rhoName rhoInf;
CofR (0 0 0);
liftDir (0 1 0);
dragDir (1 0 0);
pitchAxis (0 0 0);
magUInf 55.5; //?
lRef 0.6; //?
Aref 1; //?
outputControl outputTime;
}

What are magUInf, lRef, Aref?

Klaus

 GregorS March 6, 2011 16:58

Hi!

a.) magUInf is relative velocity between hydrofoil and water.
b.) lRef is length of hydrofoil, which is equal to chord length of hydrofoil profile.
c.) Aref is area of your hydrofoil, which is chord length*span. If you are doing 2D simulation, then span is equal to z coordinate.

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