Experimentally obtained STL file for internal Flow SnappyHexMesh
5 Attachment(s)
Hello All!
I am working on determining the best method of creating an 'educated' geometry for an internal flow application where I have an STL file from X-ray tomagraphy. I shall attempt to explain what I have done and what I would like to do. I have sized the blockMeshdict such that it smaller than my STL file in order to exclude the parts of the geometry not associated with the internal flow I am interested in. Also this is necessary since the experimentally obtained STL file is not a closed surface, so by shrinking the initial blockMesh it provides a boundary. I have taken a slice of my blockMesh with the STL file placed into it shown here, Attachment 12364. The geometry is of a 3 hole injector nozzle and this image shows the slice through one of them. By defining the blockMesh and the STL file with a cylinder around it in the geometry section of the snappyhexmeshdict I can create a suitable mesh. These can be seen here: Attachment 12365 Attachment 12366 The problem I have with this approach is that there is an excessive number of cells (2.26 million cells) and most of them are not necessary. My thought was to place a searchable sphere at the outlet to each nozzle. The geometry would look something like this. The spheres would be placed as so: Attachment 12368 In order to create a mesh that would result like this: Attachment 12367 However, at the location which the searchable sphere is intersecting with the STL file snappyhexmesh is under the impression that is the boundary to the mesh, removing the part of the STL file that appears within the sphere instead of what I am desiring with is to make the opposite end of the sphere be the boundary. The result is that half of each nozzle has been removed, but what I would rather is that the sphere be considered part of the STL and create a semisphere around the outlet. Here is the what I believe to be the pertinent parts of the snappyhexmeshdict: Code:
geometry The snappyhexmeshdict for that looked like this: Code:
geometry |
Hi Thomas;
your spheres should be within the refinementRegions section and not within the refinement surfaces. So, eventually, you should have something like this: Code:
geometry If you upload your entire snappyHexMeshDict and possibly your snappyHexMex Log or your checkMesh Log I wouldn't mind having a look. |
Attempted refinementRegion
1 Attachment(s)
Hello lovecraft22!
Thank you for your timely response. I have tried your suggestion of placing the spheres in the refinementregion section, but that still isn't doing quite what I would like. You can see here: Attachment 12370 My SHM dict file: Code:
/*--------------------------------*- C++ -*----------------------------------*\ |
What about your blockmesh? Have you tried reducing the number of cells in it?
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STL file
1 Attachment(s)
The problem is that SHM is trying to refine the mesh up against a surface for which very little flow is occuring. Shown here:
Attachment 12371 And so by trying to put an outlet semisphere on the nozzle I am trying to remove the need to mesh this surface almost entirely. |
All right, now the problem is clear!
So you basically want a coarser mesh on only a part of the surface. The fact is that all of your body gets refined in a certain way and there's no way in reducing the mesh in such zones by using a refinementRegion simply because the refinementRegion won't affect the surface mesh… So, what I would suggest you to do would be to separate your geometry in two different .stl files: one for the fine mesh and one for the coarse mesh. This way you'll get what you need. You can do this with meshlab, paraview or engrid which are free. |
Hello foamers
how can define patches for every parts of the Geometry in the .stl file? on the other hand, i created .stl file using CATIA software and import it in OpenFOAM using SHM, every things seems right, but i want to specify every parts of my Geometry by the name and patch for example Blade1,Blade2, Blade3, insideSlider and etc tnx |
Hi;
you can either separate the region you need to different stl files or create a single stl file that keeps the names of the regions and then pass these names to snappy to have different surface refinement. Have a look a these discussions: http://www.cfd-online.com/Forums/ope...e-stlfile.html http://www.cfd-online.com/Forums/ope...onditions.html http://www.cfd-online.com/Forums/ope...-tutorial.html http://www.cfd-online.com/Forums/ope...pyhexmesh.html |
great, thanks for your quick reply
so i think that is difficult work, is there a simpler solution?! tnx |
Is very easy, I don't think there's a simpler alternative.
The easiest way is that of creating different stl files. So open you original CAD file, select what will be the blade1 part, delete all of the rest, save to blade1.stl. Repeat that for blade2, blade3 and so on. If you don't have a commercial CAD software and if your geometry is not complicate then you can achieve this whole process in paraview, meshlab or engrid which are totally free. |
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