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Forces projections with moving mesh

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Old   March 19, 2015, 06:55
Default Forces projections with moving mesh
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daniel fernex
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Dear all,

I'm currently simulating a Vertical Axis Wind Turbine (VAWT) just as the one presented here : https://www.youtube.com/watch?v=-iyK5de2E1Q
I'm using OpenFoam 2.1 and the solver pimpleDyMFoam (to move the mesh). I set the controlDict so that it computes the forces and moments for each paddle. The simulation runs without issue.

BUT : I get strange forces and moments results. The problem seems to be the orientation of the forces. I got some drag that are negative when they should be positive and vice versa.

From what I've understood, the resulting force is computed by integrating the pressure on the paddle. But then how are the Drag and Lift computed from that ? So my question is : on which axis are the resulting forces projected to give Drag and Lift ?
  • Is it on the main (X,Y,Z) coordinates ? Even though the geometry rotates ?
  • Or is it on some Lift and Drag coordinates computed with the relative velocity between the paddle and the wind ?
Thanks in advance for any answer !


Regards,

Daniel
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Old   March 23, 2015, 04:39
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daniel fernex
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Hi,
I found an answer to my question : whatever is the mesh mouvement and its position, the forces are always expressed in the main coordinates (which are the (x, y, z) that can be seen in paraFoam for example). So with OF2.1 the forces are of the form :
Code:
# Time   forces(pressure, viscous) moment(pressure, viscous)
time       ((Fx Fy Fz) (Fx(visc) Fy(visc) Fz(visc)) (and so on for the moments))
Hope this helps someone.

Daniel
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