[usr0830]

Hello,
I am working on a simulation with two AMIs representing two rotors. When I use pimpleFoam, the time step size starts to decrease rapidly (from the initial deltaT=e-3 to e-23). I have tried initialising the solution with potentialFoam, the issue persists. I have also checked if the cells are connected as suggested in this post (Multiple AMI rotations not working). However, the multiSolidBodyMotionFvMesh option is unavailable on pimpleFoam 'dynamicFvMesh'.

Here is the dynamicMeshDict file.

FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "constant";
object dynamicMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dynamicFvMesh dynamicMotionSolverFvMesh;

motionSolverLibs ( "libfvMotionSolvers.so" );

motionSolver solidBody;

cellZone rotating1-cells;

solidBodyMotionFunction rotatingMotion;

origin (0 0 0);
axis (0 0 1);
omega 125; // rad/s

cellZone rotating2-cells;

solidBodyMotionFunction rotatingMotion;

origin (0.65 0 0);
axis (0 0 1);
omega -125; // rad/s
// ************************************************** *********************** //

Here is the controlDict

FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "system";
object controlDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

application pimpleFoam;

startFrom startTime;

startTime 0;

stopAt endTime;
//stopAt nextWrite;
//stopAt noWriteNow

endTime 0.5;

deltaT 1e-3;

writeControl adjustableRunTime;

writeInterval 0.002;

purgeWrite 0;

writeFormat ascii;

writePrecision 18;

writeCompression off;

timeFormat general;

timePrecision 6;

runTimeModifiable true;

adjustTimeStep yes;

maxCo 20;

functions
{
#include "forces"
}
// ************************************************** *********************** //

Any leads on why the timestep decreases to such low values would be appreciated.

Thank you.


Edit:
I also noticed that only one of my rotors (rotating2 from the dynamicMeshDict) is rotating when I ran the moveDynamicMesh -checkAMI command. I have checked with some solutions suggested for this issue on this forum but they have proved fruitless. (example: dynamicMultiMotionSolverFvMesh: This warrants an error as follows "Unknown dynamicFvMesh type dynamicMultiMotionSolverFvMesh"
mergeOrSplitBaffles -split -overwrite: This returns zero connected cells.)
Along with this, I also observe the same error message about the aspect ratio as mentioned in the https://bugs.openfoam.org/view.php?id=1026.
If anybody faced a similar issue and solved it or has any ideas about this please do chime in.

Thank you.

[Krao]

Hi, I think this is due to the number of grids in the interface, please look into the number of elements in the interface and also the overall grid size of the domain. May I know how many cells you have

Regards

[usr0830]

Originally Posted by Krao

Hi, I think this is due to the number of grids in the interface, please look into the number of elements in the interface and also the overall grid size of the domain. May I know how many cells you have

Regards

Hello Krao,
Thank you for your reply. The number of cells on each moving interface is 78 and the total number of cells in the domain is 67,766. I have the same number of cells on both sides of the moving interface.

[louisgag]

Your step size goes down because you set it according to the Courant number (here capped at 20). One of your fields probably diverges.


Try capping the Courant to 0.5 as a test and/or running the case with no rotation (but with the AMI interfaces present).