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-   -   Meshing: Smoothing Mesh for LES (http://www.cfd-online.com/Forums/star-ccm/113335-meshing-smoothing-mesh-les.html)

tobitj February 18, 2013 06:00

Meshing: Smoothing Mesh for LES
 
Hello folks,
hope you can help me!

Whats it about?:
I am new to StarCCM+ and actually trying to achieve an appropriate mesh for a LES Simulation of a channel flow (Re_t = 395). For mesh generation Iam using the triangular surface mesher & remesher and afterwards the polyhedral mesher for conversion from surface mesh into 3d polyhedral mesh. (has to be Polyhedrals)
Unfortunately my mesh has an uneven growth from edges to the center of the channel. I can see a phased and staged transition from fine mesh of the near wall area to the coarser mesh of the channel center. These visible "lines (or stages) of fineness" often proceed not parallel to the walls but diagonal into the center.

Aim: I want to attain a more smooth and homogenous mesh.

My Question:

Is there a good method of smoothing my mesh in StarCCM+ ?.


What I have already tried out:


-manipulate the triangular surface mesh without any success. (All I could achieve was to pick certain cells and remesh them / delete them -> increase mesh quality-parameters)

Thank you for your hints and advices in advance,
greetings Tobitj

tobitj February 26, 2013 03:19

Hi again,

let me ask another question that may help me:

In general is there a possibility to manipulate the 3d mesh?

I ve made the experience that all I can do is :
-use one of the surface mesher create a meshed surface.
-remesh some bad surface-cells and
-start the polyhedral volume mesher and hope for the best.

So that my only influence on the 3d Mesh is through manipulating the surface-mesh?! Is this the only possibility?

Are there any other hints to improve the quality of my 3d mesh? Something like extract surface mesh after 3d meshing then importing and redoing the remeshing process?! I am trying that at the moment.

I appreciate any kind of help here.
Thank you,

siara817 February 26, 2013 04:38

Yes, it is possible. You need to change the reference values for your meshing. Go to Continua/meshing and then click on reference values. Change the minimum and target size in a way to have almost same size. But, the question is that why do you need to have a smooth size. The mesh should be fine in walls to be solve for low Reynolds area close to the walls.

tobitj February 26, 2013 07:48

Thanks for your reply.
I want to avoid 'jumps' in cell sizes -> smoothen the cell growth in oder to minimize the truncation errors.

I played around with the surface min. sizes and target sizes but that influences only the surface mesh. My actual surface mesh has a minimum triangular face quality of 0.75.

Maybe there is a way of smoothen the grid like "laplacian smoother" in ICEM.
I recognized that STARCCM uses a octree mesher - is there a possibility of choosing an other mesher?

Another major problem is that i get a lot of low quality 3d polyhedral cells. (Cell Quality < 0.1)

ganesh_krishnan February 26, 2013 17:51

Quote:

Originally Posted by tobitj (Post 410179)
Thanks for your reply.
I want to avoid 'jumps' in cell sizes -> smoothen the cell growth in oder to minimize the truncation errors.

I played around with the surface min. sizes and target sizes but that influences only the surface mesh. My actual surface mesh has a minimum triangular face quality of 0.75.

Maybe there is a way of smoothen the grid like "laplacian smoother" in ICEM.
I recognized that STARCCM uses a octree mesher - is there a possibility of choosing an other mesher?

Another major problem is that i get a lot of low quality 3d polyhedral cells. (Cell Quality < 0.1)

you can try the boundary growth rate and template growth rate nodes..they are by default set to fast try changing it to slow...if you need a more uniform mesh, you can also use volumetric controls


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