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SimpleFoam Race Car case, solution diverges

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Old   December 2, 2012, 13:45
Question SimpleFoam Race Car case, solution diverges
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Hi

I've been using simpleFoam to analyse our FSAE car and then later develop an aero kit for it. I'm using a k-w SST model and see below for problem outline. I have 7 patches/ .obj's, 4 wheels, chassis+driver+engine, nose and side panels, and suspension. They are refined (6 7) except for the chassis which is (5 6) and each cell outside refinement region is 1m cubed.




The omega is wrong in the image, using 0.622, reduced size of boundaries as well to x=60m, y=10m, z=8m. Refinement box is also slightly reduced. So I have run it at 12.5m/s and it worked ok, you can see the residual below. I've tried many variations and simplifications of geometry, however the oscillations don't disappear. I believe this is cause by vortexes being shed from the wheels.

The blue line represents 12.5 m/s, and the red 15 m/s - basically I want Cd, Cl, and Cm values, however I want to ensure they are velocity independent which is why I'm running for velocities above and below 12.5.



The settings are identical for both except @ 20m/s, k = 0.135, w= 0.745. my fvSolution file is based off of the motorBike tutorial, and the only changes are relTol = 0.001, and tolerance is at 1e-09. fvSchemes is untouched and is identical to the motorbike case.

as you can see the solution blows up, and it happens 9 times out of 10, with different settings, I've no idea why this is happening or how I can prevent it, any help would be appreciated. I am running this case in parallel and used the scotch method for decomposing. Using 4 cores.

Last edited by GPan1; December 2, 2012 at 19:36.
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Old   December 3, 2012, 14:22
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Right so i narrowed it down and it could be the mesh causing this, I get an error with skewed faces, any help in solving, or fixing this mesh would be appreciated.

Quote:

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: 3389958
faces: 9676987
internal faces: 9472227
cells: 3148122
boundary patches: 12
point zones: 0
face zones: 0
cell zones: 0

Overall number of cells of each type:
hexahedra: 3014195
prisms: 17509
wedges: 0
pyramids: 0
tet wedges: 215
tetrahedra: 3
polyhedra: 116200

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
frontAndBack 880 1008 ok (non-closed singly connected)
inlet 80 99 ok (non-closed singly connected)
outlet 80 99 ok (non-closed singly connected)
lowerWall 36502 37661 ok (non-closed singly connected)
upperWall 550 616 ok (non-closed singly connected)
body_body 55798 61908 multiply connected (shared edge)
fl_fl 12507 13550 multiply connected (shared edge)
fr_fr 12506 13552 multiply connected (shared edge)
rl_rl 12593 13851 multiply connected (shared edge)
rr_rr 12607 13869 multiply connected (shared edge)
panels_panels 43519 45972 ok (non-closed singly connected)
sus_sus 17138 19641 multiply connected (shared edge)
<<Writing 330 conflicting points to set nonManifoldPoints

Checking geometry...
Overall domain bounding box (-10 -5 0) (45 5 8)
Mesh (non-empty, non-wedge) directions (1 1 1)
Mesh (non-empty) directions (1 1 1)
Boundary openness (-3.592883751e-20 -2.454208597e-19 3.129456631e-16) OK.
Max cell openness = 3.418154995e-16 OK.
Max aspect ratio = 77.10601231 OK.
Minumum face area = 1.154664062e-08. Maximum face area = 1. Face area magnitudes OK.
Min volume = 6.147526048e-11. Max volume = 1. Total volume = 4399.643625. Cell volumes OK.
Mesh non-orthogonality Max: 64.26771073 average: 5.590329852
Non-orthogonality check OK.
Face pyramids OK.
***Max skewness = 6.185585097, 17 highly skew faces detected which may impair the quality of the results
<<Writing 17 skew faces to set skewFaces
Coupled point location match (average 0) OK.

Failed 1 mesh checks.

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