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wing study with KomegaSST model

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Old   February 20, 2011, 06:28
Default wing study with KomegaSST model
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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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Old   February 21, 2011, 04:34
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Quote:
Originally Posted by salvoblack View Post
Failed 2 mesh checks.
Whit this mesh, you will not get any results!!!
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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Old   February 21, 2011, 06:12
Thumbs up check the aspect ratio of the mesh
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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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Old   February 21, 2011, 07:00
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"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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Old   February 21, 2011, 15:30
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but with tha spalart-Allmaras model i have good results....and i use the same mesh
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Old   February 22, 2011, 19:08
Default See this short cilp, made with simpleFoam and k-Epsilon.
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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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Old   February 23, 2011, 04:22
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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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