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[Other] OpenFOAM - structured or unstructured Grids ? |
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#1 |
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Join Date: May 2009
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Hi everybody,
For a change, I have a more general question to the community: I have been using OpenFOAM now for about 1 year and we were running in massive trouble using unstructured grids (non isothermal). We have heard now that most applications are actually on structured grids and that OF actually in reality needs structured grids. Can you confirm that? Isn't there anybody who runs complex geometries on unstructured grids? For us this would mean that we need to think about the use of an improved snappyHexMesher. Thanks a lot to you all, Thomas |
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#2 | ||
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Mark Olesen
Join Date: Mar 2009
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Quote:
Of course, a tet mesh may still give you problems. Quote:
Do the geometries pictured on page 20 of the following document qualify? http://www.opensourcecfd.com/conference2009/proceedings/documents/Session%20III/OSCIC2009_Hinterberger.pdf |
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#3 | ||
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Alberto Passalacqua
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Quote:
OpenFOAM is, in my experience, quite sensitive to the mesh quality, so you need to be a bit careful when generating the grid to avoid very skewed cells. Many of the users I saw reporting problems were using salomé or gmsh to generate their grid. They're good tools, but, in my experience, their meshing capabilities are not always the best for finite-volume codes. Quote:
Best,
__________________
Alberto Passalacqua GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats (current status: http://albertopassalacqua.com/?p=1541) OpenQBMM - An open-source implementation of quadrature-based moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using. ![]() |
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#4 |
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Yes, we saw that there was some discussion about problems with tetras, we are using the commercial mesher Centaur to generate the mesh and have some problems in particular with high aspect ratio cells...
We have also seen that OF can handle polyheder meshes, however the background of my question was that we heard that most industry projects with OF generally use an improved snappyHexMesher to generate robust meshes since OF is so sensitive to mesh quality. @Mark, yes on page 20, those would be complex geometries. I guess the iteration process to generate a good, unstructured OF mesh will just take a little bit longer... |
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#5 |
Senior Member
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For unstructured meshes with high skewness, I've seen that choice of schemes is quite important. I might recommend fvScheme settings (for simpleFoam with kOmegaSST_lowRe) such as:
//************************************************** ****** ddtSchemes { default steadyState; } gradSchemes { default cellLimited leastSquares 1.0; } divSchemes { default none; div(phi,U) Gauss reconCentral cellLimited leastSquares 1.0; div(phi,k) Gauss vanLeerDC; div(phi,omega) Gauss vanLeerDC; div(R) Gauss linear; div((nuEff*dev(grad(U).T()))) Gauss linear; } laplacianSchemes { default none; laplacian(nuEff,U) Gauss linear limited 0.5; laplacian((1|A(U)),p) Gauss linear limited 0.5; laplacian(DkEff,k) Gauss linear limited 0.5; laplacian(DomegaEff,omega) Gauss linear limited 0.5; laplacian(1,p) Gauss linear corrected; } interpolationSchemes { default reconCentral phi leastSquares; interpolate(U) reconCentral phi leastSquares; } snGradSchemes { default limited 0.5; } fluxRequired { default no; p ; } //************************************************** ****** FYI: you will need to use 1.5-dev with these settings (reconCentral doesn't exist in 1.6.x). |
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#6 |
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Ramnik Singh
Join Date: Jun 2009
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Hellp epg,
Can u please suggest similar schemes for unstructured mesh for openFoam1.6x. Thanks in Advance Ramnik |
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#7 |
Senior Member
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Ramnik,
If you want advanced functionality such as the reconCentral scheme, I would advise that you use the OpenFOAM-extend version. There is significant capability there that doesn't exist in 1.6.x or 1.7. |
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#8 | |
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Ramnik Singh
Join Date: Jun 2009
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Egp,
Changing the version is not possible as i am required to show my results for 1.6. I am running a 3D simulation for an emptying process of a surge tank design using interfoam. I have an unstructured grid and i have been facing this problem for a very long time now. The Courant's number jumps to a very high value suddenly. the mesh check is completely ok except around 230 non-orthogonal faces. here is the error Quote:
residual2.jpg Can u please have a look and suggest solution Regards Ramnik |
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#9 |
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Alberto Passalacqua
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Could you publish your fvScheme and fvSolution dictionaries?
Best,
__________________
Alberto Passalacqua GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats (current status: http://albertopassalacqua.com/?p=1541) OpenQBMM - An open-source implementation of quadrature-based moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using. ![]() |
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#10 | |
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Alberto Passalacqua
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Quote:
Thanks,
__________________
Alberto Passalacqua GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats (current status: http://albertopassalacqua.com/?p=1541) OpenQBMM - An open-source implementation of quadrature-based moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using. ![]() |
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#11 |
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Alberto Passalacqua
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I answered myself, and compiled it for 1.7.x. You find it attached (wmake libso to build it, and then include it in controlDict), but I doubt this will fix the problems you are facing, so it would still be useful to see your numerical setup.
Best,
__________________
Alberto Passalacqua GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats (current status: http://albertopassalacqua.com/?p=1541) OpenQBMM - An open-source implementation of quadrature-based moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using. ![]() |
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#12 |
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BastiL
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#13 | |
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Alberto Passalacqua
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Quote:
vanLeerDC is the vanLeer scheme with deferred correction. I never used them in OF since they're not in the 1.7.x, but I am a bit doubtful about the improvements they can bring on poor meshes. Sometime it is just easier to fix the mesh than waste time fiddling with schemes. You'll also gain in quality of the results. Best,
__________________
Alberto Passalacqua GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats (current status: http://albertopassalacqua.com/?p=1541) OpenQBMM - An open-source implementation of quadrature-based moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using. ![]() |
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#14 |
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BastiL
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Thanks Alberto. So it is a modification of "linear" in terms that it still is cental differencing and second order?
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#15 |
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ms
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Well, I'm interested in the reconCentral approach now, too. My openFoam is version 2.1.0 and I downloaded it for Ubuntu without building it. My questions are....
1) Is openFoam-ext still going? The website shows little / no forum activity that I could see. 2) Can I insert components from openFoam-ext into openFoam 2.1.0, given that I didn't build it? 3) Do openFoam-ext components find their way into openFoam after time or is it completely separate? (This seems a little odd, given the open/free nature of the code). Best regards all, Mark. |
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#16 | ||||
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Alberto Passalacqua
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Quote:
Quote:
Quote:
Quote:
Best,
__________________
Alberto Passalacqua GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats (current status: http://albertopassalacqua.com/?p=1541) OpenQBMM - An open-source implementation of quadrature-based moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using. ![]() |
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#17 | |
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andres
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Thanks! Andrés |
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#18 | |
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sirshosona
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#19 |
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Tobias Adam
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Hello everyone
What settings for unstructured Mesh do you prefer for people who don´t use the extended version of OpenFoam? Greets Tobi |
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#20 |
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Bharadwaj Bhushan
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hi Alberto,
can you suggest me which meshing tool is best suited for openFoam ? Thank you |
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