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-   -   rotatingWallVelocity bc (http://www.cfd-online.com/Forums/openfoam/79950-rotatingwallvelocity-bc.html)

Lodda September 9, 2010 06:42

rotatingWallVelocity bc
 
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

madad2005 September 9, 2010 07:30

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.

Lodda September 9, 2010 07:54

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.

http://img21.imageshack.us/img21/8669/rotcylinder.jpg

Best regards

Lodda

madad2005 September 9, 2010 08:23

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.

Lodda September 9, 2010 08:33

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 :)

madad2005 September 9, 2010 08:47

Heh, no worries. It's a surprisingly easy mistake to make!

davidmd September 12, 2010 02:41

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 :)

sheikh nasir February 14, 2012 08:53

train moving in tunnel
 
hello ,
can any body help me as i am getting floating error: invalid number. my email sheikhnasir39@gmail.com
with regards:confused:


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