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Old   August 24, 2015, 11:16
Default Aerodynamic Coefficients
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Sukratu Barve
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I am using sonicFOAM for a not very unsteady flow. I am using a 3D geometry for aerospace applications. The solver is working on the case and appears to be giving
proper screen messages. Now I wanted the aerodynamic coefficients and realized
that the controlDIct file has lines which make the solver record only lift, drag and moment coefficients, which may be used for 2D geometries. There are however, six such
coefficients in all for me with my 3D case. Nobody seems to have required all six, perhaps! I did not find anything regarding that on the net! Any help would be appreciated.
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Old   August 24, 2015, 13:24
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Hassan Kassem
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Sorry but your question is not clear, which coefficients you want to compute?
Generally, If they are direction based, just define new forceCoeffs functionObject with different directions. OR you could develop new function object for that.
Otherwise if you are looking to compute different coefficients based on force type, you can define in controlDict forces functionObject and calculate the coefficient based on these pressure and viscous forces. Also it is possible to develop new functionObject for this purpose.
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Old   August 25, 2015, 11:21
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Sukratu Barve
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I need to calculate the following aerodynamic coefficients:
Drag Coeff.(C_D)
Lift Coeff.(C_L)
Side Force Coeff. (C_S)
Rolling Moment Coeff. (C_l)
Pitching Moment Coeff.(C_m)
Yawing Moment Coeff. (C_n)

The syntax for the lines to be included in controlDict for lift and drag
seem to be

liftDir (1 ,1 ,1 );
dragDir (1,0,1);

and there is a line to take in the pitching axis

pitchDir (0,0,1) ;
which presumably give the direction about which the moment of the "moment" coefficient in two dimensions is calculated.

(Please ignore the details of the directions above. I have cooked them up just to
explain which lines I mean)

Now do I simply say something like

yawDIr (0,1,0);

to obtain the yawing coefficient ?

Or will I have to ask the solver to give me force components and moment components
in a file and obtain the coefficients separately by shell scripting and formulae code files? Right now, that seems to be the best option for me. But something like

sideforceDir (1,0,0);

would be fabulous
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Old   August 25, 2015, 11:27
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Sorry it is not pitchDir but pitchAxis.
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Old   August 25, 2015, 11:44
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Sukratu Barve
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Apparently this works. Will try it over tomorrow and post back on this thread.

Adding side force to forceCoeffs.C

Last edited by wyldckat; August 26, 2015 at 17:54. Reason: merged posts that were a few minutes apart
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Old   August 25, 2015, 12:19
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Without even modifying the source code you can define two functionObjects for coefficient in controlDict with different directions and axis.
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Old   August 25, 2015, 12:57
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Will try that as well.
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Old   August 26, 2015, 11:15
Default Error during wmake operation
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Sukratu Barve
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We seem to get problems during wmake. I have mentioned those in the following thread

Adding side force to forceCoeffs.C
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