[Lodda]

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]

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]

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

[madad2005]

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]

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]

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

[davidmd]

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]

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

[viraj20feb]

Originally Posted by madad2005

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.

Greetings!

I am wanted ask to what do you mean by 'make sure your origin is in the right place'? I also have an annulus-type geometry in which the inner cylinder is rotating. Also, if we look at the source code:
const vectorField Up
(
(-om)*((patch().Cf() - origin_) ^ (axis_/mag(axis_)))
);

Shouldn't the distance be the perpendicular distance from the axis rather than the distance between the face center and the origin?

Thanks
Viraj