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SRF Solution issue with Prism+Tetra mesh compare to Hexa

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Old   February 22, 2013, 16:32
Default SRF Solution issue with Prism+Tetra mesh compare to Hexa
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Hi friends,
i m solving a periodic section problem (9.72 deg section) using SRF model, inititally i solved the problem with the pure hexa (coarse- 0.1 million) i got consistent results but now i m trying to add vortex generator on blade, therefore i have to mesh domain with tetra+prism (0.6 million) and i did it, but i m not getting proper results, residuals are also fluctuating, and getting very high velocity on periodic patches. I tried with only tetra also but faced same issue. Even trying with different discretization scheme. Please suggest me the better discretization scheme. can i use hex-core mesh from tgrid to foam....

Thank you In advance....
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Old   February 25, 2013, 13:59
Default inccorect results with tetra compare to hex mesh for the same case
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Hi friends,
i m solving a periodic flow problem using SRF model, inititally i solved the problem with the hexa mesh (coarse- 0.1 million) i got good results for various cases, but when same case i m trying with tetra+prism mesh (fine-0.6 million), then i m not getting proper results, residuals are also fluctuating, and getting very high velocity on periodic patches...please help me out...any one has clue regarding these....kindly waiting for reply...

nitin
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Old   February 25, 2013, 19:00
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Greetings Nitin,

You're not sharing much information on your problem, so it'll be very hard for anyone to help you.
The best I can do to help is give you some sources of information:
Best regards and good luck!
Bruno
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Old   February 26, 2013, 16:24
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Hi thanks for your reply.. Actually im trying to match results of Case-II (tetra+prism mesh) with Case-I (Hexa mesh).
I m solving a periodic flow problem for fan (Axial entry & radial exit) and i have taken single blade periodic section (from total of 37 blades). Simulation details area as follows:

Case I.) Initialy i tried with hexa mesh (periodic hexa mesh from ICEM):
cell count: 0.09 million
checkMesh: OK for all criterias
Steady state flow
Inlet: velocity inlet (Urel=20.4m/s)
Outlet: pressure outlet (0)
Model: SRFSimpleFoam (as i have only one cell zone i.e. rotating one)
Turbulence Model: SST K-W
Descretization schemes:- grad(p):Gauss linear;
grad(Urel):Gauss linear;
div(phi,Urel) Gauss upwind
laplacianSchemes: Gauss linear corrected

Output: impeller efficiency:57%

Case II) In case-2, I tried with tetra+prism on blade mesh (Periodic mesh)
checkMesh: Number of severly non orthogonal faces:46 and Non-orthogonality check: OK, also remaining checkmesh criterias are ok
Cell count: 0.6 million
"All remaining settings are same like Case-I"
Output: Solution getting diverging and giving very high velocity throughout domain, even though Residuals are dropping below 0.01.

kindly waiting for reply...Thanks in dvance

Nitin
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Old   February 27, 2013, 04:58
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Hi Nitin,

What does checkMesh tell you about the mesh that has tetrahedral cells?
And are you using non-orthogonal correctors?

Best regards,
Bruno
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Old   February 27, 2013, 14:06
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Hi Bruno, Thanks for your reply, quality check for Tet+Prism mesh is given below,,,,

administrator@ubuntu:~/nitin/ME/ME/results/0.2/1.3tetraFinePrism$ checkMesh
/*---------------------------------------------------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 2.1.1 |
| \\ / A nd | Web: www.OpenFOAM.org |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
Build : 2.1.1-221db2718bbb
Exec : checkMesh
Date : Feb 27 2013
Time : 12:54:26
Host : "ubuntu"
PID : 2233
Case : /home/administrator/nitin/ME/ME/results/0.2/1.3tetraFinePrism
nProcs : 1
sigFpe : Enabling floating point exception trapping (FOAM_SIGFPE).
fileModificationChecking : Monitoring run-time modified files using timeStampMaster
allowSystemOperations : Disallowing user-supplied system call operations

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
Create time

Create polyMesh for time = 0

Time = 0

Mesh stats
points: 121835
faces: 1233760
internal faces: 1169262
cells: 594532
boundary patches: 7
point zones: 0
face zones: 1
cell zones: 1

Overall number of cells of each type:
hexahedra: 0
prisms: 24630
wedges: 0
pyramids: 264
tet wedges: 0
tetrahedra: 569638
polyhedra: 0

Checking topology...
Boundary definition OK.
Cell to face addressing OK.
Point usage OK.
Upper triangular ordering OK.
Face vertices OK.
Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces ...
Patch Faces Points Surface topology
outlet 2256 1297 ok (non-closed singly connected)
inlet 2290 1263 ok (non-closed singly connected)
blade 8210 2137 multiply connected (shared edge)
hub 4986 2841 ok (non-closed singly connected)
shroud 4280 2392 ok (non-closed singly connected)
left1 21238 10836 ok (non-closed singly connected)
right1 21238 10836 ok (non-closed singly connected)
<<Writing 2134 conflicting points to set nonManifoldPoints

Checking geometry...
Overall domain bounding box (-0.0201298 0 -7.68958e-26) (0.0850515 0.306492 0.1787)
Mesh (non-empty, non-wedge) directions (1 1 1)
Mesh (non-empty) directions (1 1 1)
Boundary openness (1.74928e-19 4.05201e-20 -7.65942e-20) OK.
Max cell openness = 2.21344e-16 OK.
Max aspect ratio = 13.0933 OK.
Minumum face area = 5.08171e-08. Maximum face area = 8.40055e-06. Face area magnitudes OK.
Min volume = 8.5903e-12. Max volume = 7.97833e-09. Total volume = 0.000920781. Cell volumes OK.
Mesh non-orthogonality Max: 78.1445 average: 16.2617
*Number of severely non-orthogonal faces: 42.
Non-orthogonality check OK.
<<Writing 42 non-orthogonal faces to set nonOrthoFaces
Face pyramids OK.
Max skewness = 1.27209 OK.
Coupled point location match (average 1.22399e-11) OK.

Mesh OK.

Time = 1

Mesh stats
points: 121835
faces: 1233760
internal faces: 1169262
cells: 594532
boundary patches: 7
point zones: 0
face zones: 1
cell zones: 1

Overall number of cells of each type:
hexahedra: 0
prisms: 24630
wedges: 0
pyramids: 264
tet wedges: 0
tetrahedra: 569638
polyhedra: 0

Checking topology...
Boundary definition OK.
Cell to face addressing OK.
Point usage OK.
Upper triangular ordering OK.
Face vertices OK.
Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces ...
Patch Faces Points Surface topology
outlet 2256 1297 ok (non-closed singly connected)
inlet 2290 1263 ok (non-closed singly connected)
blade 8210 2137 multiply connected (shared edge)
hub 4986 2841 ok (non-closed singly connected)
shroud 4280 2392 ok (non-closed singly connected)
left1 21238 10836 ok (non-closed singly connected)
right1 21238 10836 ok (non-closed singly connected)
<<Writing 2134 conflicting points to set nonManifoldPoints

Checking geometry...
Overall domain bounding box (-0.0201298 0 -7.68958e-26) (0.0850515 0.306492 0.1787)
Mesh (non-empty, non-wedge) directions (1 1 1)
Mesh (non-empty) directions (1 1 1)
Boundary openness (1.74928e-19 4.05201e-20 -7.65942e-20) OK.
Max cell openness = 2.21344e-16 OK.
Max aspect ratio = 13.0933 OK.
Minumum face area = 5.08171e-08. Maximum face area = 8.40055e-06. Face area magnitudes OK.
Min volume = 8.5903e-12. Max volume = 7.97833e-09. Total volume = 0.000920781. Cell volumes OK.
Mesh non-orthogonality Max: 78.1445 average: 16.2617
*Number of severely non-orthogonal faces: 42.
Non-orthogonality check OK.
<<Writing 42 non-orthogonal faces to set nonOrthoFaces
Face pyramids OK.
Max skewness = 1.27209 OK.
Coupled point location match (average 1.22399e-11) OK.

Mesh OK.

End




In fvSolution file i m using following settings for orthogonal corrector

SIMPLE
{
nNonOrthogonalCorrectors 0;
}

Kindly waiting for your reply.

Regards
Nitin
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Old   February 27, 2013, 17:57
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Hi Nitin,

Try setting "nNonOrthogonalCorrectors" to 2:
Code:
nNonOrthogonalCorrectors 2;
At least it's what I've seen in the forum...

Nonetheless, these messages:
Quote:
<<Writing 2134 conflicting points to set nonManifoldPoints
...
*Number of severely non-orthogonal faces: 42.
are a source of concern. The effect of the second one might be reduced with the "nNonOrthogonalCorrectors", but it probably will only reduce the error level by a little bit.
The first one... I don't know. Check if your other mesh had these issues as well or not.

If possible, I would advise you to generate a new mesh with improved quality.

Best regards,
Bruno
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