Ansys: Unstructured Solver
 

Hi everybody,

the Ansys CFX Solver is an unstructured solver and a structured mesh will always be dealt with internally as an unstructured Mesh (Ansys Help, Reference Guide, 2.1 Valid Mesh Elements). Does this mean, that the Ansys CFX Solver will always convert a structured grid with a neighbor connectivity table/array (i,j,k) to an unstructured grid with node location and neighbor connection tables/arrays?

If this question is answered with "yes", whats the point in using a structured mesh with Ansys CFX if its advantage, the efficient structured storage, is lost due to the conversion to an unstructured mesh?

I hope my question is clear.

Kind Regards

If the mesh is structured with I,J,K storage, it very likely is a hexahedral mesh; therefore, it is greatly advantageous using this type of meshes for the efficient modeling of boundary layer flows.

Thanks for your reply,

so the hexahedral mesh is advantageous for the modelling of boundary layer flows even if its not structured stored?

Because according to the Ansys CFX documentary, the Ansys CFX Solver handles the structured Mesh internally as unstructured Mesh, so it is not longer structured with I,J,K storage? That was my question in the first place.

Kind regards

The IJK thing is just how you identify a specific element in a structured mesh. CFX does not use this, it uses an unstructured notation.

But a structured mesh can be a high quality mesh with good element orthogonality, aspect ratio and size gradation. This is why a structured mesh can be superior to an unstructured mesh, even in an unstructured solver.

Thanks a lot!

So the hexahedral mesh tends to have higher quality.

I guess this would reduce numerical diffusion for example?

But in terms of computational time, would the Ansys CFX Solver be slower then a structured solver?

Regards

I would say hexahedral meshes CAN have higher quality. If the geometry is simple blocks then generating a high quality hex mesh is easy, but generating a quality hex mesh in a complex 3D geometry is difficult. In some complex geometry it is not possible to generate a high quality hex mesh - in these cases a good unstructured mesh is better than a poor quality structured mesh.

Higher mesh quality = reduced numerical diffusion. This is true.

CFX will be slower than a structured solver of similar quality as unstructured solvers have to untangle a complex element connectivity matrix, but a structured solver only needs to handle simple IJK notation. This leads to significant speed differences.

Thats all I wanted to know, I appreciate your fast and clear answers. Thanks a lot!