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February 20, 2011, 05:28
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wing study with KomegaSST model
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#1 |
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Member
Join Date: Oct 2010
Location: Naples
Posts: 50
Rep Power: 15  |
hi,
I am making the study of a 3D mesh with simpleFoam solver and turbulence model KomegaSSt. Problem is that I get the values of Cl and Cd very high. could you give me a hand, especially as regards the values to be assigned ake omega? Add my case, and even the checkMesh Create time Create polyMesh for time = 0 Time = 0 Mesh stats points: 306577 faces: 896256 internal faces: 873216 cells: 294912 boundary patches: 4 point zones: 0 face zones: 1 cell zones: 1 Overall number of cells of each type: hexahedra: 294912 prisms: 0 wedges: 0 pyramids: 0 tet wedges: 0 tetrahedra: 0 polyhedra: 0 Checking topology... Boundary definition OK. Point usage OK. <<Found 72 neighbouring cells with multiple inbetween faces. Upper triangular ordering OK. <<Writing 144 unordered faces to set upperTriangularFace Face vertices OK. Number of regions: 1 (OK). Checking patch topology for multiply connected surfaces ... Patch Faces Points Surface topology frontAndBack 9216 9432 ok (non-closed singly connected) farfield2 3072 3153 ok (non-closed singly connected) farfield1 6144 6273 ok (non-closed singly connected) wall 4608 4681 ok (non-closed singly connected) Checking geometry... Overall domain bounding box (-6.373 -7.373 -6.37538) (7.4107 0 6.37538) Mesh (non-empty, non-wedge) directions (1 1 1) Mesh (non-empty) directions (1 1 1) Boundary openness (-3.19694e-16 -1.77267e-18 -8.55767e-17) OK. ***High aspect ratio cells found, Max aspect ratio: 103701, number of cells 7562 <<Writing 7562 cells with high aspect ratio to set highAspectRatioCells Minumum face area = 2.213e-08. Maximum face area = 1.44338. Face area magnitudes OK. Min volume = 7.43982e-11. Max volume = 0.44983. Total volume = 886.796. Cell volumes OK. Mesh non-orthogonality Max: 89.1138 average: 20.1794 *Number of severely non-orthogonal faces: 2382. Non-orthogonality check OK. <<Writing 2382 non-orthogonal faces to set nonOrthoFaces Face pyramids OK. ***Max skewness = 16.6197, 210 highly skew faces detected which may impair the quality of the results <<Writing 210 skew faces to set skewFaces Failed 2 mesh checks. End As you can see, i have 2 check failed, but i don't think that i could be a great problem because in fluent with the same mesh i have good results |
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February 21, 2011, 03:34
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#2 | |
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Senior Member
maddalena
Join Date: Mar 2009
Posts: 436
Rep Power: 23 |
Quote:
I guess there have been some troubles when exporting the mesh from fluent (is it really the same mesh???). My suggestion is to load your mesh in paraview and check where the problem is. I think you will find some cells which are not as you designed. mad |
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February 21, 2011, 05:12
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check the aspect ratio of the mesh
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#3 |
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Member
kiran Ambilpur
Join Date: Jun 2010
Location: India
Posts: 50
Rep Power: 15  |
Hi salvoblack.
one thing i found the from my experience of conversion of mesh from Fluent to foam. it gives errors. i suggest you to use blockmeshDict tool or any any other OpenFOAm mesh tool for meshing its is easy to learn. Even i suggest you one more thing like, the distance between two grid points is more at the farfield. so reduce the distance (increase the no of grid points accordingly) try this. i did not see the case which you have attached but i decoded the error from your post. try the things which i said you... all the best. hope fully use k-epsilon for best results Reagrds Ambilpur Kiran |
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February 21, 2011, 06:00
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#4 |
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Senior Member
Anonymous
Join Date: Mar 2009
Posts: 110
Rep Power: 17 |
"hope fully use k-epsilon for best results"
I would not reccommend using the k-epsilon turbulence model for achieving any form of accuracy for aerodynamic configurations such as a wing, where the skin friction drag accounts for such a high percentage of the total drag. k-omega based turbulence models are known to perform much better, with or without wall functions. |
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February 21, 2011, 14:30
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#5 |
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Member
Join Date: Oct 2010
Location: Naples
Posts: 50
Rep Power: 15 |
but with tha spalart-Allmaras model i have good results....and i use the same mesh
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February 22, 2011, 18:08
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See this short cilp, made with simpleFoam and k-Epsilon.
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#6 |
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Member
Rickard Hidefjäll
Join Date: Jun 2009
Location: Uppsala, Sweden
Posts: 39
Rep Power: 16 |
http://www.youtube.com/watch?v=DVhBxnNRj8Q
http://www.youtube.com/watch?v=6UgRDLMLZ2E I have just today made the same simulation with kOmegaSST. And it worked much better. The clip is about a forward swept wing with stream lines. One from a front view And the other from a back view. Regards / Rickard Hidefjäll |
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February 23, 2011, 03:22
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#7 |
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Member
Join Date: Oct 2010
Location: Naples
Posts: 50
Rep Power: 15 |
yes, but i don't think that it can be useful for me...
in any case i resolved my problem. i changed the data in the fvscheme using a new corrector. thanks to everyone |
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