Calculating Lift and Drag in Paraview (paraFoam)
Hi there,
I have a body that I wish to extract the lift and drag forces for in Paraview. I assume that this can be achieved using the calculator but I cannot work it out. Could someone please give me some pointers on this. Basically I need to calculate the normals for each surface, then find the pressure on each surface in the components of X (or Y or Z, depending on if it is Drag, Lift or side force), then intergrate these values for the whole body to get the Force value. If someone has a procedure for something like this then please let me know! Thanks for your help, Scott 
I found a solution:
Extract Surfaces Generate Surface Normals Use the calculator to multiply pressure by the surface normals (Normals*p) This then prints the values in the data tab at the right in three columns, one for each normal direction. I then integrate these to get total forces on the area using Integrate Variables. Let me know if you see any problems with this approach! Cheers, Scott 
Hey Scott,
I am trying to do the same thing and am attempting your approach. I was just wondering if you've made any more progress since you posted. I'd like to collaborate with you if possible. 
Scott,
Where (and how) do you calculate the area of each panel? I'm struggling finding a particularly good way of doing this. Right now I'm performing a similar calculation in Fortran, but I would prefer to do this in paraview. 
Any advances on this? Also, how would you go about including the effect of skin friction? I guess the wallShearStress postpro function would be a start.

lift and drag coeffs in paraview
Hi
How can I calculate lift and drag coefficient in paraview? I've run an oscillating airfoil with pitching motion.I've calculated lift and drag coefficient through libforces in controlDict, but the values are wrong. I want to calculate them in paraview and plot them over the time or angle. Please tell me how to do this? 
In 2D, you might want to try something like this in paraview on the surfaces you want to evaluate,
1. filter: generate surface normals (disable splitting, activate compute cell normals) 2. filter: calculator using something like this for moments : Normals_Y*p*yourDensity*(yourCoRx16) + Normals_X*p*yourDensity*(yourCoRycoordsY) replacing yourDensity and yourCoR* by appropriate values or simplify it to get forces 3. filter: integrate variables and look for the results of the integration in the table that appears in the end this procedure gives you sum_cells(P*rho*A*norm_y) I think this can be easily adapted to 3D. cheers 
I've had some success working with cell data (as opposed to point data) on 3D surface meshes, if it's of use:
Cell area can be obtained using the Mesh Quality filter and the Area option. Use the Point Data to Cell Data on your pressure data. Then use Generate Surface Normals (may need to Extract Surface first) with the Compute Cell Nomals option enabled. Pop these into a calculator using the Cell Data mode and that should have you on the right track for the pressure side of things. 
Hello louisgag, could you please explain what do you mean by "yourCoR"?
Thank you very much. 
Center of Rotation
Regards, Louis 
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Thank you very much. 
Thank you for your quick reply.
Another question if you don't mind, So, If my center of rotation is (0,0,0), Does this mean that CoRx=0, and CoRy=0? Sorry if the question is too simple, I am new to CFD. 
Yes, that is correct.
Louis 
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May I ask why it's 16 in your equation: Normals_Y*p*yourDensity*(yourCoRx16) + Normals_X*p*yourDensity*(yourCoRycoordsY) ? Another quenstion is about the center of rotation in paraView. My understanding is that the center of the geometry will be the center of rotation. please correct me if I am wrong. It will be very appreciated if you can indicate how to get or display the coordinates of the center of rotation. Thank you very much in advance! 
Hi Bruce,
I'm pretty sure that's a typo, and should read "coordsX" thanks for noting it I'll correct it. Regards, Louis 
Hi Louis,
Thank you very much for your prompt reply. It's clear now. By the way, I found a way to get the center of rotation: simply click the Probe Location button in the tool bar and the 'Center' followed by three values in the Properties tab would be the Center of Rotation used in the equation. If you cannot find the Probe Location button in your tool bar, go to the main menu, then Fliters>Data Analysis>Probe Location, you will get the same thing. This may be very redundant for experienced ParaView user, but I think it should be helpful for newbie of ParaView, like me. Cheers, Bruce 
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