Meshing a rotating torus within another Torus for CFD

  • Last Post 20 November 2018
  • Topic Is Solved
sebastian1991 posted this 17 November 2018


for a Research Projekt, I am currently trying to calculate the air resistance of a rotating Torus which is encased inside another Torus with Ansys Fluent in a transient model. The following picture I hope describes what I want to achieve:


I get the model to run on a small scale in Fluent with very low accuracy.

However, the final Torus will have a Diameter of around 100 Meter and can hardly be scaled down any further in diameter and dimensions. When meshing this system with the needed accuracy and Tetragonal Cells, I end up with around 20.000.000+ Cells, which is why I try to find ways reducing the cell-count.

Currently I am trying two different methods to reduce the cell count:

1. Using Multizone/Hex-Dominant Meshing combined with sizing functions. The Problem is, that the contact region of the sliding mesh will never be meshed accurately and Ansys gives warnings.

2. Make use of the Axial Symmetry of the System and only mesh 180/90/45 degree of the Torus with applying "cyclic symmetry" to the system. With this approach, the sliding mesh will constantly "rotate out of the boundaries"


Inflations Layers are already on both of the walls.

Is there any other way to scale down a system like this, or to mesh it more efficiently?

Any help or hints will be highly appreciated



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kkanade posted this 19 November 2018

Please do not use hex dominant method of cfd. 

Please use multizone or sweep method. 

For using these methods, you may need to slice the model at some locations. 

sebastian1991 posted this 20 November 2018

Thank you very much for your answer.

I have actually already tried out this method.

The Torus in standard is not sweepable. Slicing the Torus makes it sweepable and the generated mesh looks a lot better. However Ansys can not convert this mesh to Fluent because of errors in the contact region. I suppose that is because both of my geometries are Enclosures . But however I try to slice the body or built the geometry, the error consists.

kkanade posted this 20 November 2018

Errors in contact region?

Please create a single part with all bodies in DM or SpaceClaim so that you will get conformal mesh for Fluent. Pleas suppress contact regions in meshing. Then proceed to Fluent. 

sebastian1991 posted this 20 November 2018

Suppressing the contact region did the trick!

Thank you so much, I have been breeding over this for weeks now))

kkanade posted this 20 November 2018

Glad that it worked. Can you mark this as 'Is Solution' to help others on forum.