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Old   September 9, 2010, 06:42
Default rotatingWallVelocity bc
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Hi Foamers,

i try to calculate a flow between two cylinders. The inner cylinder is rotating so i used the rotatingWallVelocity bc for the inner wall.

My 0/U file:

dimensions [0 1 -1 0 0 0 0];

internalField uniform (0 0 0);

boundaryField
{
movingWall
{
type rotatingWallVelocity;
origin (0 0 0);
axis (0 0 1);
omega 25;
}

fixedWall
{
type fixedValue;
value uniform (0 0 0);
}

frontandback
{
type empty;
}
}

Paraview shows that the rotating wall velocity is exact twice bigger then expected.
The diameter of the inner cylinder is 0.035 m OpenFoam wall velocity 0.875 m/s.
What is the unit of omega in the U ?

Thanks an best regards

Lodda
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Old   September 9, 2010, 07:30
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velocity (m/s) = omega (1/s) * radius (m)

Are you using the cylinder diameter or the radius to compute the rotational velocity? That could be why your velocity is twice as big as you were expecting.
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Old   September 9, 2010, 07:54
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The OpenFoam result for the rotating wall velocity is 0.875 m/s. I expected according to v = omega * r = 25 * 0.0175 = 0.4375 m/s. I dont know what is wrong.

boundaryField
{
movingWall
{
type rotatingWallVelocity;
origin (0 0 0);
axis (0 0 1);
omega 25;
value nonuniform List<vector>
200
(
(0.0137422 -0.874784 0)
(0.0412131 -0.873921 0)
(0.0686432 -0.872195 1.86596e-27)
(0.0960057 -0.869609 -0)
(0.123273 -0.866164 0)
(0.150419 -0.861864 0)

This are the components of the calculated velocity. The magnitude at the rotating wall is always 0.875 m/s.



Best regards

Lodda
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Old   September 9, 2010, 08:23
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Ok, one thing to check (which I am sure you have done) is that the diameter you are using is correct. Second is to make sure your origin is in the right place. What am I looking at in the image? Do you have a cylinder within a cylinder? Apart from this, I'm a bit stumped tbh. I have it working without an issue on a more complex problem that this one.
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Old   September 9, 2010, 08:33
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This are two cylinders and the inner cylinder is rotating with omega = 25 as explained above and thats it.

Sorry, i checked my blockMeshdict the diameter is wrong!

Thanks for answering
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Old   September 9, 2010, 08:47
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Heh, no worries. It's a surprisingly easy mistake to make!
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Old   September 12, 2010, 02:41
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Lodda, I'm trying to simulate cylinder with rotating bottom, filled with a viscous laminar incompressible fluid. Your case is very similar to mine. Maybe you could send me your files, because I'm new to OpenFOAM, and can not figure out how I do it.
Sorry for my English
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Old   February 14, 2012, 08:53
Default train moving in tunnel
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hello ,
can any body help me as i am getting floating error: invalid number. my email sheikhnasir39@gmail.com
with regards
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