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-   -   SimpleFoam Race Car case, solution diverges (http://www.cfd-online.com/Forums/openfoam/109993-simplefoam-race-car-case-solution-diverges.html)

GPan1 December 2, 2012 13:45

SimpleFoam Race Car case, solution diverges
 
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.

http://i49.tinypic.com/2qstrmf.jpg


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.

http://i50.tinypic.com/29zf03p.jpg

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.

GPan1 December 3, 2012 14:22

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.

End


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