[joyw]

[Figure 1]

Hi, I am new to Openfoam and I am trying to run a simulation on a model shown in Figure 1.
The dimensions of the computational domain are 0.1 m x 0.1 m x 0.1 m and there is a cylinder of length 0.05 m, outer diameter 0.02 m and inner diameter 0.01 m at the center.
I’m trying to spin the cylinder as shown in Figure 2.


[Figure 2]

I ran the simulation using simpleFoam (I'm using OpenFoam version 2.3.0.) and specified the information on the rotational motion in fvoptions.
After setting all the control values to 0.001 in the residual control, the results seem to show excessive velocities.
The following (Figure 3) is an YZ cross-section. Given the outer radius of 0.02 m and rotational speed of 3.1416 rad/s, the maximum fluid velocity comes out to be 0.351 m/s. Simple hand calculation would show that the maximum fluid velocity should be around 0.0628 m/s (radius x rot. speed).


[Figure 3]

The mesh used in this test is shown below. The mesh is made up of simple tetrahedrals. The red circle is where the cylinder is placed.


[Figure 4]

The following is what I specified in fvoptions.

MRF1
{
type MRFSource;
active yes;
selectionMode cellZone;
cellZone cellTable_2;

MRFSourceCoeffs
{
// Fixed patches (by default they 'move' with the MRF zone)
//nonRotatingPatches ();

origin (0 0 0);
axis (0 1 0);
omega constant 3.14159265358979;
}
}

In order to obtain a more reasonable result, what are the issues that I need to resolve and if there is anything wrong with the above specifications, please let me know. Thank you.

[jackpap]

Hi, if you are trying to spin a solid annular cylinder :

1. You shouldn't have mesh inside the solid part (unless you're doing some Conjugate Heat Transfer simulation...)
2. You shouldn't need an MRF. A simple rotatingWallVelocity boundary condition on your cylinder walls should do the trick.

If the solid annular cylinder is only the "MRF ZONE" then what / where is the rotating geometry you are simulating?

Good luck.

[joyw]

Thank you for your reply.
It seems there has been a misunderstanding due to a lack of explanation.
What I am trying to simulate is a simplified/modeled mixer, rather than a solid annular cylinder. (For reference, the fluid is simply water). So what can be done in this case?

[jackpap]

In figure 3 how come we can't see the solid outline of the mixer blades ?

[joyw]

It's just a simple model simulating the motion of the mixer without actually modeling the blades, simply giving tangential velocity components to the flow around it.

[Ben UWIHANGANYE]

Hello,

Hope you are well!


May you help on this case?
Indeed i want to move a solid cylinder, I have coded in c++ the equation of motion(simple harmonic equation). The cylinder was created using cylinderTocell in topoSetDict.

Can you help to know how make that cylinder oscillating using that equation.

or if you know another way to use to make that cylinder oscillating without dynamic mesh, i will be happy to hear from you.

Attached is the c++ equation of motion.



Regard!

Thank you.