Learning Forum

[constantina]

Hello everyone,

I'm working on an numerical analysis of transient flow past two rotating circular cylinders at Re=100 in Ansys Fluent. Firstly, I ran the first case with the only one cylinder rotating (the other one was stationary) and I got the correct results. But, when I defined extra the second cylinder as a moving wall, I got the following message: 

WARNING: The wall motion has a significant normal component on 78 faces of face zone 10.

The maximum angle between the velocity and face surface is 89.2 deg at ( 4.221e-01, 4.926e-01, 0.000e+00).

The tolerance for this check is controlled by the rpvar 'wall/vnormal-tolerance'.

Please check your setup. This warning will not be written again.

I have set the motion as "relative to adjacent cell zone" in both boundary conditions. (I don't know if this is related somehow.)
The reference frame has been defined at the center of the one cylinder.
Does anyone know something about this warning and what probably can I do to fix it?
Thank you in advance!

[Sunil Lilhare]

Hello, the warning you're encountering in Ansys Fluent regarding the wall motion having a significant normal component suggests that the wall boundary conditions may not be set up correctly for the rotating zone. This could be due to an incorrect specification of the rotation axis or the rotation rate, which is causing the wall to have a velocity component normal to the face, rather than tangential.

 

To resolve this issue, you should check the following:

 

1. Ensure that the rotation-axis origin is set correctly. It should typically be set to 0,0,0 unless your geometry requires a different origin.

 

2. Verify that the boundary conditions for the wall are set to 'moving wall' and that the settings are consistent with the rotating domain. If you are using the 'Relative to adjacent cell zone' formulation, the angular speed should be set to 0 rad/s. For 'absolute' formulation, ensure that the angular speed is set correctly.

 

3. If the rotating domain contains static walls, then the walls should be configured to have zero velocity in the absolute reference frame.

 

4. Check that the walls set as Rotating Wall are axisymmetric if the steady-state physics are to be valid.

 

For more information please refer to the link of a section of Ansys Fluent User Guide given below.

10.3. Flow in Multiple Moving Reference Frames (ansys.com)

[constantina]

 

 

 

Thank you for your prompt response. This is a 2d unsteady flow. Both cylinders have to be moving. I haven’t set sliding mesh, or dynamic mesh. Also, I’ve set one fluid domain and it is stationary. Because you mentioned “rotating domain”, my case is to investigate the flow past two rotating cylinders. There are not rotating domains. I’ve just set the boundary conditions on these two walls, as moving walls with rotating motion. I have set one reference frame, the global one (as it seems in the screenshots). So far, I haven't found what I should do.

 

 

[Sunil Lilhare]

Yes, previously described steps are for rotating cell zones. In your case, the warning you're encountering indicates that the wall motion in your simulation has a significant component normal to the surface of the faces in face zone. This could be due to the setup of the rotating wall boundary conditions, where the specified motion does not align well with the actual face orientations. To resolve this, you should check the boundary conditions for the rotating walls to ensure they are defined correctly and align with the intended physical setup. Adjusting the 'wall/vnormal-tolerance' rpvar value may also help, but it's crucial to ensure that the physical model is correct first.

Please check the link below and refer to section 7.4.15.4 to know more about rotating wall boundary condition.

7.4. Boundary Conditions (ansys.com)