[chakshu]

Hello all,


I am trying to simulate a propeller (8 inch diameter) for UAV drone purposes using SRFSimpleFoam. I am following the mixer tutorial (tutorials/incompressible/SRFSimpleFoam/mixer) in the OpenFoam Tutorials.

I have exported the mesh from Ansys and converted it to openfoam format using Fluent3DMeshtoFoam. I have 180 degree domain consisting single propeller.

The changes which I did as compared to mixer tutorial are following:

• changing the cyclic BC to cyclicAMI on side boundaries because of mismatch between number of faces in meshing.

In the results, I am getting insanely huge values for pressure forces, and also time step continuity errors are very large (of order 1e+40).


I am pretty sure something is wrong but I am not able to find it. The same problem has been discussed in this post. But, I could not spot a suiatble answer for SRFSimpleFoam.


After 2-3 timesteps, it stops the simultation with the following error.

Time = 4

smoothSolver:  Solving for Urelx, Initial residual = 0.846793, Final residual = 0.0760998, No Iterations 121
smoothSolver:  Solving for Urely, Initial residual = 0.868998, Final residual = 0.0776762, No Iterations 124
smoothSolver:  Solving for Urelz, Initial residual = 0.847657, Final residual = 0.0822867, No Iterations 122
DICPCG:  Solving for p, Initial residual = 1, Final residual = 1.40252e+19, No Iterations 1000
time step continuity errors : sum local = 1.81742e+40, global = 2.16988e+39, cumulative = 2.16988e+39
smoothSolver:  Solving for omega, Initial residual = 2.42954e-08, Final residual = 2.42954e-08, No Iterations 0
smoothSolver:  Solving for k, Initial residual = 0.131845, Final residual = 0.00493715, No Iterations 2
ExecutionTime = 1472.1 s  ClockTime = 1472 s

forces forces write:
    Sum of forces
        Total    : (2.43156e+37 1.36295e+36 -1.8984e+37)
        Pressure : (2.43156e+37 1.36295e+36 -1.8984e+37)
        Viscous  : (1.82323e+29 8.15445e+28 3.86707e+29)
    Sum of moments
        Total    : (1.19196e+35 -4.22212e+35 -5.27805e+35)
        Pressure : (1.19196e+35 -4.22212e+35 -5.27805e+35)
        Viscous  : (6.54475e+27 4.03697e+27 -4.80881e+27)


Time = 5

#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::symGaussSeidelSmoother::smooth(Foam::word const&, Foam::Field<double>&, Foam::lduMatrix const&, Foam::Field<double> const&, Foam::FieldField<Foam::Field, double> const&, Foam::UPtrList<Foam::lduInterfaceField const> const&, unsigned char, int) at ??:?
#4  Foam::symGaussSeidelSmoother::smooth(Foam::Field<double>&, Foam::Field<double> const&, unsigned char, int) const at ??:?
#5  Foam::smoothSolver::solve(Foam::Field<double>&, Foam::Field<double> const&, unsigned char) const at ??:?
#6  Foam::fvMatrix<Foam::Vector<double> >::solveSegregated(Foam::dictionary const&) at ??:?
#7  Foam::fvMatrix<Foam::Vector<double> >::solveSegregatedOrCoupled(Foam::dictionary const&) at ??:?
#8  Foam::fvMesh::solve(Foam::fvMatrix<Foam::Vector<double> >&, Foam::dictionary const&) const at ??:?
#9  ? in ~/OpenFOAM/OpenFOAM-v1912/platforms/linux64GccDPInt32Opt/bin/SRFSimpleFoam
#10  __libc_start_main in /lib/x86_64-linux-gnu/libc.so.6
#11  ? in ~/OpenFOAM/OpenFOAM-v1912/platforms/linux64GccDPInt32Opt/bin/SRFSimpleFoam
Exception en point flottant (core dumped)

The picture of mesh is attached with this post. Can someone help me spot where is the mistake. Let me know if you need more details in order to understand the problem.

[chakshu]

Hello,

Update:
I changed nNonOrthogonalCorrectors to 1 from 0. It allowed to run the simulations a little longer. I tried for like 2000 timesteps. And it ran fine untill then. But when I monitor the forces, the forces tends to diverge to higher values (although not very unrealistics). This simulation I was doing with komegaSST.

Then, I tried the simulation with Sparat-Allmaras to simplify the things. I try to ran with same configuration with 2000 timesteps. But the simulation crashes at aroung 1600th iteration with very high value of forces (e+28) . Could someone pleaes help me with this problem?

For the checkMesh, I get the following results with 2 probelms namely, unusedpoints and skewness:

Checking topology...
    Boundary definition OK.
    Cell to face addressing OK.
 ***Unused points found in the mesh, number unused by faces: 312580 number unused by cells: 312580
  <<Writing 312580 unused points to set unusedPoints
  <<Found 9 neighbouring cells with multiple inbetween faces.
    Upper triangular ordering OK.
  <<Writing 18 unordered faces to set upperTriangularFace
    Face vertices OK.
    Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces...
                   Patch    Faces   Points                  Surface topology
                   inlet     3288     4763  ok (non-closed singly connected)
                  outlet     3289     4761  ok (non-closed singly connected)
                  shroud     6194    10320  ok (non-closed singly connected)
                   blade   169642   339115  ok (non-closed singly connected)
                te_blade    25743    51466  ok (non-closed singly connected)
                   per_2    19451    38904  ok (non-closed singly connected)
                   per_1    19372    38746  ok (non-closed singly connected)
                    axis    64271   128546  ok (non-closed singly connected)

Checking faceZone topology for multiply connected surfaces...
                FaceZone    Faces   Points                  Surface topology
         interior--fluid 28952453 15389613  multiply connected (shared edge)
  <<Writing 15389071 conflicting points to set nonManifoldPoints

Checking basic cellZone addressing...
                CellZone        Cells       Points       VolumeBoundingBox
                  fluid      7200315     15389617     0.102393 (-0.254 -2.053e-18 -0.4064) (0.254 0.253922 0.6096)

Checking geometry...
    Overall domain bounding box (-0.254 -1.38778e-17 -0.4064) (0.254 0.253994 0.6096)
    Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
    Mesh has 3 solution (non-empty) directions (1 1 1)
    Boundary openness (-1.59155e-16 1.18998e-14 -1.40174e-16) OK.
    Max cell openness = 1.03043e-15 OK.
    Max aspect ratio = 85.4444 OK.
    Minimum face area = 1.43191e-14. Maximum face area = 0.00041943.  Face area magnitudes OK.
    Min volume = 2.17485e-18. Max volume = 8.79784e-06.  Total volume = 0.102393.  Cell volumes OK.
    Mesh non-orthogonality Max: 80.455 average: 12.7295
   *Number of severely non-orthogonal (> 70 degrees) faces: 6074.
    Non-orthogonality check OK.
  <<Writing 6074 non-orthogonal faces to set nonOrthoFaces
    Face pyramids OK.
 ***Max skewness = 4.83049, 252 highly skew faces detected which may impair the quality of the results
  <<Writing 252 skew faces to set skewFaces
     Coupled point location match (average 0) OK.

I am not sure if the skewness could lead to such divergence. Kindly help me with any leads. Thanks in advance.

Regards,

Chakshu

[damon707]

Hello Chaksu,

Did you manage to do this simulation on the propeller??? I'm also trying to stimulate a wind turbine rotor with SRFSimplefoam as the solver and I would really appreciate some insight...

Best,
George

[chakshu]

Hi George,


I could not manage to make the simulation converge with SRFSimpleFoam, but it was okay with MRFSimpleFoam. Instead of using a symmetrical blade, I used the complete blade and used MRF. Atleast simulation converge with that.

[damon707]

Could you please share with me the boundary conditions you used?

[chakshu]

Hi,

Sorry for the late reply. Can you please share you email (if you still needs the files)? Or drop a message at deorachakshu03@gmail.com. I am unable to attach the files here.

However, the thrust and torque from the simulation were under predicitng as compared to experiments within 15-20% range, as I explain in this post.