| azam13 |
March 2, 2015 09:55 |
Simple 3D External Flow Around A Sphere
Hi everyone,
I am currently working on a project which requires me to utilise openFOAM to study flow around object. I think I should mention here that my knowledge in CFD is limited. I have used ANSYS CFX before, and I had full instructions when I ran a specific case using CFX. But now I'm on my own.
I am using gmsh (I don't get to choose meshing software) to mesh the fluid domain and then import the mesh into openFOAM. The flow around the sphere is laminar at Re=500 and I am using the simpleFoam solver.
However, I have tried setting up a case, but encountered problems upon running it. For weeks, I have tried using various methods of set up I copied from other cases, either from openFOAM itself or from what I found online. None of those methods worked, and I decided it would be easier for me to post here. Below is the log of the error I have encountered.
Code:
Time = 2.1
smoothSolver: Solving for Ux, Initial residual = 0.570575, Final residual = 0.0181165, No Iterations 16
smoothSolver: Solving for Uy, Initial residual = 0.569282, Final residual = 0.0310181, No Iterations 20
smoothSolver: Solving for Uz, Initial residual = 0.411578, Final residual = 0.0145823, No Iterations 20
GAMG: Solving for p, Initial residual = 0.974154, Final residual = 0.0663001, No Iterations 4
GAMG: Solving for p, Initial residual = 0.999972, Final residual = 1.69907e-10, No Iterations 1
time step continuity errors : sum local = 4.61607e+11, global = -2.80841e+08, cumulative = -2.80841e+08
ExecutionTime = 66.57 s ClockTime = 79 s
Time = 2.2
smoothSolver: Solving for Ux, Initial residual = 0.571405, Final residual = 0.0558804, No Iterations 4
smoothSolver: Solving for Uy, Initial residual = 0.571405, Final residual = 0.0181964, No Iterations 6
smoothSolver: Solving for Uz, Initial residual = 0.571405, Final residual = 0.0189882, No Iterations 6
GAMG: Solving for p, Initial residual = 1, Final residual = 0.09372, No Iterations 4
GAMG: Solving for p, Initial residual = 1, Final residual = 2.48991e-11, No Iterations 1
time step continuity errors : sum local = 1.88144e+30, global = 5.84363e+25, cumulative = 5.84363e+25
ExecutionTime = 69.18 s ClockTime = 82 s
Time = 2.3
smoothSolver: Solving for Ux, Initial residual = 0.410403, Final residual = 8.89009e+10, No Iterations 1000
smoothSolver: Solving for Uy, Initial residual = 0.411742, Final residual = 1.17565e+12, No Iterations 1000
smoothSolver: Solving for Uz, Initial residual = 0.410765, Final residual = 3.90412e+11, No Iterations 1000
#0 Foam::error::printStack(Foam::Ostream&) at ??:?
#1 Foam::sigFpe::sigHandler(int) at ??:?
#2 in "/lib/x86_64-linux-gnu/libc.so.6"
#3 Foam::GAMGSolver::scale(Foam::Field<double>&, Foam::Field<double>&, Foam::lduMatrix const&, Foam::FieldField<Foam::Field, double> const&, Foam::UPtrList<Foam::lduInterfaceField const> const&, Foam::Field<double> const&, unsigned char) const at ??:?
#4 Foam::GAMGSolver::Vcycle(Foam::PtrList<Foam::lduMatrix::smoother> const&, Foam::Field<double>&, Foam::Field<double> const&, Foam::Field<double>&, Foam::Field<double>&, Foam::Field<double>&, Foam::Field<double>&, Foam::Field<double>&, Foam::PtrList<Foam::Field<double> >&, Foam::PtrList<Foam::Field<double> >&, unsigned char) const at ??:?
#5 Foam::GAMGSolver::solve(Foam::Field<double>&, Foam::Field<double> const&, unsigned char) const at ??:?
#6 Foam::fvMatrix<double>::solveSegregated(Foam::dictionary const&) at ??:?
#7 Foam::fvMatrix<double>::solve(Foam::dictionary const&) at ??:?
#8
at ??:?
#9
at ??:?
#10 __libc_start_main in "/lib/x86_64-linux-gnu/libc.so.6"
#11
at ??:?
Floating point exception (core dumped)
https://www.dropbox.com/s/vkxs1ohwux2lly5/Forum?dl=0
Below is a plot of the residuals:
https://www.dropbox.com/s/tssy0g71h1...Forum.png?dl=0
As you can see, the residuals and time step continuity errors shot up abruptly.
If it helps, below is a visual of my mesh. The cut plane is parallel to the inlet and outlet surfaces.
https://www.dropbox.com/s/i5s9qgyeahied7z/mesh.png?dl=0
Below is the log of the checkMesh.
Code:
Mesh stats
points: 112989
faces: 1208580
internal faces: 1144764
cells: 588336
faces per cell: 4
boundary patches: 7
point zones: 0
face zones: 0
cell zones: 1
Overall number of cells of each type:
hexahedra: 0
prisms: 0
wedges: 0
pyramids: 0
tet wedges: 0
tetrahedra: 588336
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
sphere 36064 18034 ok (closed singly connected)
outlet 1800 953 ok (non-closed singly connected)
back 6000 3117 ok (non-closed singly connected)
inlet 1808 957 ok (non-closed singly connected)
front 6064 3149 ok (non-closed singly connected)
top 6072 3153 ok (non-closed singly connected)
bottom 6008 3121 ok (non-closed singly connected)
Checking geometry...
Overall domain bounding box (-5 -1 -1) (13 4 4)
Mesh (non-empty, non-wedge) directions (1 1 1)
Mesh (non-empty) directions (1 1 1)
Boundary openness (-2.05954e-16 -1.55549e-15 9.59819e-17) OK.
Max cell openness = 3.47786e-15 OK.
Max aspect ratio = 239.478 OK.
Minimum face area = 2.58373e-06. Maximum face area = 0.0908523. Face area magnitudes OK.
Min volume = 1.05397e-08. Max volume = 0.00525295. Total volume = 449.477. Cell volumes OK.
Mesh non-orthogonality Max: 89.6467 average: 31.0267
*Number of severely non-orthogonal (> 70 degrees) faces: 11391.
Non-orthogonality check OK.
<<Writing 11391 non-orthogonal faces to set nonOrthoFaces
Face pyramids OK.
Max skewness = 1.42164 OK.
Coupled point location match (average 0) OK.
Mesh OK.
My boundaries set up is as following:
For p: everything (inlet, top, bottom, sides) zeroGradient, except outlet with fixedValue 0.
For U: inlet fixedValue uniform (0.0005 0 0), wall fixedValue uniform (0 0 0), on sides and top and bottom I used slip, outlet is zeroGradient.
My fvScheme is:
Code:
ddtSchemes
{
default steadyState;
}
gradSchemes
{
default Gauss linear;
}
divSchemes
{
default none;
div(phi,U) bounded Gauss linearUpwind grad(U);
div(phi,nuTilda) bounded Gauss linearUpwind grad(nuTilda);
div((nuEff*dev(T(grad(U))))) Gauss linear;
}
laplacianSchemes
{
default Gauss linear corrected;
}
interpolationSchemes
{
default linear;
}
snGradSchemes
{
default corrected;
}
fluxRequired
{
default no;
p ;
}
My fvSolutions is:
Code:
solvers
{
p
{
solver GAMG;
tolerance 1e-05;
relTol 0.1;
smoother GaussSeidel;
nPreSweeps 0;
nPostSweeps 2;
cacheAgglomeration true;
nCellsInCoarsestLevel 10;
agglomerator faceAreaPair;
mergeLevels 1;
}
U
{
solver smoothSolver;
smoother GaussSeidel;
nSweeps 2;
tolerance 1e-05;
relTol 0.1;
}
}
SIMPLE
{
nNonOrthogonalCorrectors 1;
pRefCell 0;
pRefValue 0;
residualControl
{
p 1e-5;
U 1e-5;
// nuTilda 1e-5;
}
}
relaxationFactors
{
fields
{
p 0.3;
}
equations
{
U 0.7;
// nuTilda 0.7;
}
}
Are there any mistakes, especially in fvScheme and fvSolutions? Those are the two files on which I have the least knowledge. It could also be because of the non-orthogonality of the mesh too, though I have applied corrector of value 1. Also, it would be appreciated if fellow forumers can suggest how I can simulate the top, bottom and sides as far field instead of slip. Thank you for your time and help! Please let me know if you need more information. :)
Regards,
Azam |
