Cylinder subjected to a flow: Dynamic mesh problems

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  • Last Post 18 June 2018
dan_123 posted this 04 June 2018

Hello everyone,

I am trying to simulate a cantilever cylinder subjected to a fluid flow (3D) using 2-way FSI.  The expected displacement is less than 2 times the diameter of the cylinder (in my case, 10 mm) so I decided to simulate this displacement on the tip of the cylinder in still water to check the mesh deformation and this is where I'm trapped.

I separated the fluid in two zones: one around the cylinder to capture the boundary layer, and the other with the rest of the fluid. Both have cylindrical shapes. In dynamical mesh, I selected the smoothing (spring on all cells) and layering method. The spring method allowed me to select "Deform adjacent boundary layer with zone", which maintains the shape of the boundary layer zone.

\i have two types of problems depending on if I select "share" or "group" between fluid zones in the "shared topology" section in Spaceclaim:

Group topology:

- The "boundary layer fluid" zone penetrates the "rest of the fluid" zone as the cylinder moves. It's like both zones were detached. I find this weird since its the same material (water) and fluent recognises it as an interface zone.

Share topology:

- The "rest of the fluid" zone moves along with the movement of the cylinder+"boundary layer" zone. It doesn't absorb it in the interface region between zones. I can see that the cells along the outer wall of my model absorb the motion, which is problematic. In addition, it seems that the layering method doesn't work since I don't see any splitting of collapsing cells throughout the movement.

Sorry for the long post. In summary, my goal is to create a mesh that is able to absorb the cylinder's movements and, to preserve a high quality boundary layer zone.

 

I attached an image to clarify my problem. This is just a test, that's why the mesh is not decent.

Attached Files

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kkanade posted this 11 June 2018

Hello dan_123

Layering option will not be useful in your case. It is mainly for applications like piston-cylinder. 

Please see below the example of setting up 2 way fsi problem. 

Regards,

Keyur

dan_123 posted this 18 June 2018

Thanks Keyour,

 

I've seen those videos before but they do not address the boundary layer problem I have.I think, for my case, I have two options

 

- Use the linearly elastic solid method and accept that the boundary layer around the cylinder will deform as the cylinder moves.

- Use the Spring method with the correct deformation parameters to avoid negative cell volumes. Use "deform adjacent boundary layer with zone for the fluid near the cylinder and use tetra mesh to absorb the deformation due to the cylinder movement.

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