[soup]

Hi,

I have never used openfoam before. I want to simulate a deformable body on a microscopic scale. This means I need to solve incompressible viscous flow at low reynolds number in an infinite space.

Can someone point me in the right direction as to what solver I should be looking at or any other tips ? I'm also fairly new to fluid dynamics so if something i've said doesn't make sense I am happy to clarify.

Thanks,

Bryan

[msrinath80]

Perhaps icoFoam or simpleFoam. But if you want to study deformations, I think you might need to look into DynFoam or some such. Have you searched the forum for similar cases?

[soup]

Thank you for your reply.

I have searched the forum and the internet for information on low reynolds number simulation in openFoam and I haven't been able to find anything saying whether current solvers in openFoam are capable of this.

How can I find out whether icoFoam or simpleFoam will work?

[msrinath80]

If the flow is laminar, icoFoam or one its moving mesh capable variants (search the forum, there are a good number of folks working on moving mesh) will do just fine. If you're referring to low-Re turbulence models, there is info out here[1].

[1] http://www.opencfd.co.uk/openfoam/tu...tml#turbulence

[soup]

Just to clarify with laminar flow icoFoam will work even at very low reynolds number?

[msrinath80]

Totally. It should in principle at least. Or maybe is there a stokes solver around in OpenFOAM?

[eugene]

If the Re number is really really low, just remove the convection term, + fvm::div(phi, U), from icoFoam's Ueqn and recompile. Instant Stokes flow.

[soup]

The re number that i want to simulate is very low. I tried the idea of removing fvm::div(phi, U) from icoFoam and recompiling but I now get this error when I run icoFoam:

--> FOAM FATAL IO ERROR : Unknown symmetric matrix solver BICCG

Valid symmetric matrix solvers are :

4
(
ICCG
GaussSeidel
DCG
AMG
)


file: /home/bryan/OpenFOAM/bryan-1.2/run/tutorials/potentialFoam/lowrecylinder/system/ fvSolution::U at line 28.

From function lduMatrix::solver::New(const fvMesh&, Istream&)
in file matrices/lduMatrix/lduMatrixSolver.C at line 100.

FOAM exiting

I have not changed the fvSolution file and if I put the line back in and recompile if works fine once again.

Does anyone have any ideas as to what may be wrong? I am not very familiar with c++ so I may be missing something obvious that is done by this line.

Are there any other ways of acheiving creeping flow in openFoam?

[hjasak]

Yes. OpenFOAM knows whether the matrix you have assembled is symmetric or assymetric. For symmetric matrices it will use symmetric matrix solvers, which are prettier, faster etc. than assymetric solvers.

When your equation contains the convection term, you will have an assymetric matrix, which requires an assymetric solver, e.g. BiCCG. When you remove it, the matrix will be symmetric and you need to use a symmetric solver, for example ICCG - this is exactly what the error message says.

Enjoy,

Hrv