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January 27, 2010, 13:47 |
Rotating cylinder
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#1 |
New Member
Join Date: Jan 2010
Posts: 4
Rep Power: 16 |
Hi everyone,
I just started to use OpenFOAM and am currently studying the "Flow around a cylinder" tutorial. Suppose I want to see the effect of having the cylinder rotate. This would easily be configured by setting the boundary to moving wall and specifying the angular velocity. Is this possible? I have read about mesh motion mechanisms, but they seem like overkill in this case, since the mesh is not moving, only the cylinder wall is. Any help appreciated. Thanks, Ole |
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January 27, 2010, 16:44 |
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#2 |
Member
Patricio Bohorquez
Join Date: Mar 2009
Location: Jaén, Spain
Posts: 95
Rep Power: 17 |
That is an interesting problem. Could you use GGI boundary condition on the "inside" cylinder and keep us posted? You could try something similar to mixerGgi that lives into OpenFOAM-1.5-dev/tutorials/icoDyMFoam.
Thanks, Patricio. |
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January 27, 2010, 17:19 |
Using GGI changes problem to an unsteady one
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#3 |
New Member
Join Date: Jan 2010
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Using GGI changes (as far as I understand) the problem to an unsteady one. I am interested in the steady solution, just like in the tutorial for the cylinder flow, except the cylinder should rotate with a constant speed. This amounts to setting the tangential velocity of the cylinder boundary to some uniform value, and then solving the steady problem. I can set the velocity on the boundary uniformly to some constant vector in cartesian coordinates, but is it possible to set the tangential velocity to some constant?
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January 28, 2010, 11:32 |
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#4 | |
Senior Member
Andrea Pasquali
Join Date: Sep 2009
Location: Germany
Posts: 142
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You can try with this BC in U file
Quote:
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Andrea Pasquali |
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January 28, 2010, 12:54 |
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#5 |
New Member
Join Date: Jan 2010
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Works perfectly! Thank you.
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February 2, 2010, 10:54 |
rotatingWallVelocity or MRFsimpleFoam
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#6 |
Senior Member
maddalena
Join Date: Mar 2009
Posts: 436
Rep Power: 23 |
Hello everybody,
I am wondering if a simpleFoam with a rotatingWallVelocity BC simulation can replace a MRFsimpleFoam simulation. They both are steadyState but:
Thanks to those that will shed some light! mad |
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February 10, 2010, 05:45 |
Solved!
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#7 |
Senior Member
maddalena
Join Date: Mar 2009
Posts: 436
Rep Power: 23 |
Ok, I find the answer with the help of a young woman far more expert in cfd modeling than me.
The rotatingWall BC applies the rotation only the flow that is in contact with the wall, since it is a boundary condition. This will propagate to the adjacent cells but the rotating effect will be under-predicted since these cells have their own velocity that has no rotation component. This can be ok if the wall is simple, i.e. there are no blades on the rotating body. This is ok for the rotating cylinder case of this thread. On the other hand, the MFR approach considers as rotating the whole flow volume around the wall. This case is more adequate if the rotating body has blades. Indeed, the flow between two blades has almost the same velocity of the blades themselves. The MRF approach is ok if the mean flow far from the rotating body is wanted, or if the blade number is high, since the steady field values can be obtained only. If the blade number is low, the pressure pulse generated by the blade rotation cannot be discarded and a dynamicMesh approach should be used. Hope to be useful to someone else. Cheers, maddalena |
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