[rahulksoni]

I am sharing an interesting observation of the performance of OpenFOAM solver. I also seek suggestions from users/developers on why it is happening.

I wanted to perform a moving mesh simulation for my stirred mill equipment for which I considered the pimpleDyMFoam/propeller tutorial as the most suitable one. I tried to study the tutorial configuration with the best of my understanding. Its a turbulent case with k, nut, epsilon models.
Then step by step I have modified the case according to my needs. The changes primarily includes:
1. The parametric changes on innerCylinder, outerCylinder and innerCylinderSmall.
2. The design of propeller.
3. Inlet, outlet are now behave like walls. So, instead of having inlet/outlet for fluid flow we have a closed chamber filled with fluid.
4. The whole domain has some porosity value.
The new design looks something like attached. The dimensions of the outer cylinder is 20cm (height) by 20 cm (diameter).
Rest of the things remain same.

Then, I have performed the simulation with original moving mesh rotation of 158 rad/sec, which works ok. A pimpleDyMFoam logfile is attached for the reference. Some simulation snapshots are also attached.

Then, I reduced the speed (rpm) of the stirrer/propeller to 105 rad/sec keeping everything else same, and observed that it stops at around 0.0012 sec due to high courant number issue or convergence issue.

In general, courant number issue should occur at higher propeller rpm as it increases the fluid velocity and therefore courant number for given mesh sizes. However, in my case the issues appears for lower rpm.
The output procuses error of something like below:

Courant Number mean: 1.0125e+18 max: 1.30092e+22
deltaT = 2.03476e-48
Time = 0.00128044

solidBodyMotionFunctions::rotatingMotion::transformation(): Time = 0.00128044 transformation: ((0 0 0) (0.997741 (0 0.0671727 0)))
AMI: Creating addressing and weights between 25292 source faces and 25680 target faces
AMI: Patch source sum(weights) min/max/average = 0.938494, 1.06474, 1.00013
AMI: Patch target sum(weights) min/max/average = 0.943794, 1.01665, 0.999925
PIMPLE: iteration 1
- selecting cells using cellZone porosity1
- selected 89136 cell(s) with volume 0.002766
- selecting cells using cellZone porosity1
- selected 89136 cell(s) with volume 0.002766
smoothSolver:  Solving for Ux, Initial residual = 0.916696, Final residual = 0.0906739, No Iterations 9
smoothSolver:  Solving for Uy, Initial residual = 0.839402, Final residual = 0.0208579, No Iterations 1
smoothSolver:  Solving for Uz, Initial residual = 0.944621, Final residual = 0.0898537, No Iterations 4
- selecting cells using cellZone porosity1
- selected 89136 cell(s) with volume 0.002766
GAMG:  Solving for p, Initial residual = 1, Final residual = 6.40357e+54, No Iterations 50
time step continuity errors : sum local = 8.03351e+50, global = 1.00568e+48, cumulative = 1.00568e+48
- selecting cells using cellZone porosity1
- selected 89136 cell(s) with volume 0.002766
PIMPLE: iteration 2
- selecting cells using cellZone porosity1
- selected 89136 cell(s) with volume 0.002766
- selecting cells using cellZone porosity1
- selected 89136 cell(s) with volume 0.002766
smoothSolver:  Solving for Ux, Initial residual = 6.01472e-12, Final residual = 6.01472e-12, No Iterations 0
smoothSolver:  Solving for Uy, Initial residual = 1.21862e-11, Final residual = 1.21862e-11, No Iterations 0
smoothSolver:  Solving for Uz, Initial residual = 8.41206e-12, Final residual = 8.41206e-12, No Iterations 0
- selecting cells using cellZone porosity1
- selected 89136 cell(s) with volume 0.002766
[0] #0  [2] #0  Foam::error::printStack(Foam::Ostream&)Foam::error::printStack(Foam::Ostream&) at ??:?
 at ??:?
[0] #1  [2] #1  Foam::sigFpe::sigHandler(int)Foam::sigFpe::sigHandler(int) at ??:?
[0] #2  ? at ??:?
[2] #2  ? in "/lib/x86_64-linux-gnu/libc.so.6"
[0] #3  Foam::DICPreconditioner::calcReciprocalD(Foam::Field<double>&, Foam::lduMatrix const&) in "/lib/x86_64-linux-gnu/libc.so.6"
[2] #3  Foam::DICPreconditioner::calcReciprocalD(Foam::Field<double>&, Foam::lduMatrix const&) at ??:?
[0] #4  Foam::DICSmoother::DICSmoother(Foam::word const&, Foam::lduMatrix const&, Foam::FieldField<Foam::Field, double> const&, Foam::FieldField<Foam::Field, double> const&, Foam::UPtrList<Foam::lduInterfaceField const> const&) at ??:?
[2] #4  Foam::DICSmoother::DICSmoother(Foam::word const&, Foam::lduMatrix const&, Foam::FieldField<Foam::Field, double> const&, Foam::FieldField<Foam::Field, double> const&, Foam::UPtrList<Foam::lduInterfaceField const> const&) at ??:?
[0] #5  Foam::DICGaussSeidelSmoother::DICGaussSeidelSmoother(Foam::word const&, Foam::lduMatrix const&, Foam::FieldField<Foam::Field, double> const&, Foam::FieldField<Foam::Field, double> const&, Foam::UPtrList<Foam::lduInterfaceField const> const&) at ??:?
[2] #5  Foam::DICGaussSeidelSmoother::DICGaussSeidelSmoother(Foam::word const&, Foam::lduMatrix const&, Foam::FieldField<Foam::Field, double> const&, Foam::FieldField<Foam::Field, double> const&, Foam::UPtrList<Foam::lduInterfaceField const> const&) at ??:?
[0] #6  Foam::lduMatrix::smoother::addsymMatrixConstructorToTable<Foam::DICGaussSeidelSmoother>::New(Foam::word const&, Foam::lduMatrix const&, Foam::FieldField<Foam::Field, double> const&, Foam::FieldField<Foam::Field, double> const&, Foam::UPtrList<Foam::lduInterfaceField const> const&) at ??:?
[2] #6  Foam::lduMatrix::smoother::addsymMatrixConstructorToTable<Foam::DICGaussSeidelSmoother>::New(Foam::word const&, Foam::lduMatrix const&, Foam::FieldField<Foam::Field, double> const&, Foam::FieldField<Foam::Field, double> const&, Foam::UPtrList<Foam::lduInterfaceField const> const&) at ??:?
[2] #7  Foam::lduMatrix::smoother::New(Foam::word const&, Foam::lduMatrix const&, Foam::FieldField<Foam::Field, double> const&, Foam::FieldField<Foam::Field, double> const&, Foam::UPtrList<Foam::lduInterfaceField const> const&, Foam::dictionary const&) at ??:?
[0] #7  Foam::lduMatrix::smoother::New(Foam::word const&, Foam::lduMatrix const&, Foam::FieldField<Foam::Field, double> const&, Foam::FieldField<Foam::Field, double> const&, Foam::UPtrList<Foam::lduInterfaceField const> const&, Foam::dictionary const&) at ??:?
[2] #8  Foam::GAMGSolver::initVcycle(Foam::PtrList<Foam::Field<double> >&, Foam::PtrList<Foam::Field<double> >&, Foam::PtrList<Foam::lduMatrix::smoother>&, Foam::Field<double>&, Foam::Field<double>&) const at ??:?
[0] #8  Foam::GAMGSolver::initVcycle(Foam::PtrList<Foam::Field<double> >&, Foam::PtrList<Foam::Field<double> >&, Foam::PtrList<Foam::lduMatrix::smoother>&, Foam::Field<double>&, Foam::Field<double>&) const at ??:?
[2] #9  Foam::GAMGSolver::solve(Foam::Field<double>&, Foam::Field<double> const&, unsigned char) const at ??:?
[0] #9  Foam::GAMGSolver::solve(Foam::Field<double>&, Foam::Field<double> const&, unsigned char) const at ??:?
 at ??:?
[2] #10  Foam::fvMatrix<double>::solveSegregated(Foam::dictionary const&)[0] #10  Foam::fvMatrix<double>::solveSegregated(Foam::dictionary const&) at ??:?
[2] #11   at ??:?
[0] #11  Foam::fvMatrix<double>::solve(Foam::dictionary const&)Foam::fvMatrix<double>::solve(Foam::dictionary const&) at ??:?
[2] #12   at ??:?
[0] #12  ?? at ??:?
[2] #13  __libc_start_main at ??:?
[0] #13  __libc_start_main in "/lib/x86_64-linux-gnu/libc.so.6"
[2] #14  ? in "/lib/x86_64-linux-gnu/libc.so.6"
[0] #14   at ??:?
[MSLab02:31637] *** Process received signal ***
[MSLab02:31637] Signal: Floating point exception (8)
[MSLab02:31637] Signal code:  (-6)
[MSLab02:31637] Failing at address: 0x3e800007b95
?[MSLab02:31637] [ 0] /lib/x86_64-linux-gnu/libc.so.6(+0x3ef20)[0x7f255715af20]
[MSLab02:31637] [ 1] /lib/x86_64-linux-gnu/libc.so.6(gsignal+0xc7)[0x7f255715ae97]
[MSLab02:31637] [ 2] /lib/x86_64-linux-gnu/libc.so.6(+0x3ef20)[0x7f255715af20]
[MSLab02:31637] [ 3] /home/mslab02/OpenFOAM/OpenFOAM-3.0.x/platforms/linux64GccDPInt32Opt/lib/libOpenFOAM.so(_ZN4Foam17DICPreconditioner15calcReciprocalDERNS_5FieldIdEERKNS_9lduMatrixE+0x134)[0x7f2558457d84]
[MSLab02:31637] [ 4] /home/mslab02/OpenFOAM/OpenFOAM-3.0.x/platforms/linux64GccDPInt32Opt/lib/libOpenFOAM.so(_ZN4Foam11DICSmootherC1ERKNS_4wordERKNS_9lduMatrixERKNS_10FieldFieldINS_5FieldEdEESB_RKNS_8UPtrListIKNS_17lduInterfaceFieldEEE+0x12c)[0x7f255845467c]
[MSLab02:31637] [ 5] /home/mslab02/OpenFOAM/OpenFOAM-3.0.x/platforms/linux64GccDPInt32Opt/lib/libOpenFOAM.so(_ZN4Foam22DICGaussSeidelSmootherC1ERKNS_4wordERKNS_9lduMatrixERKNS_10FieldFieldINS_5FieldEdEESB_RKNS_8UPtrListIKNS_17lduInterfaceFieldEEE+0x4b)[0x7f25584557db]
[MSLab02:31637] [ 6] /home/mslab02/OpenFOAM/OpenFOAM-3.0.x/platforms/linux64GccDPInt32Opt/lib/libOpenFOAM.so(_ZN4Foam9lduMatrix8smoother30addsymMatrixConstructorToTableINS_22DICGaussSeidelSmootherEE3NewERKNS_4wordERKS0_RKNS_10FieldFieldINS_5FieldEdEESE_RKNS_8UPtrListIKNS_17lduInterfaceFieldEEE+0x48)[0x7f2558455aa8]
[MSLab02:31637] [ 7] /home/mslab02/OpenFOAM/OpenFOAM-3.0.x/platforms/linux64GccDPInt32Opt/lib/libOpenFOAM.so(_ZN4Foam9lduMatrix8smoother3NewERKNS_4wordERKS0_RKNS_10FieldFieldINS_5FieldEdEESB_RKNS_8UPtrListIKNS_17lduInterfaceFieldEEERKNS_10dictionaryE+0x237)[0x7f2558445877]
[MSLab02:31637] [ 8] /home/mslab02/OpenFOAM/OpenFOAM-3.0.x/platforms/linux64GccDPInt32Opt/lib/libOpenFOAM.so(_ZNK4Foam10GAMGSolver10initVcycleERNS_7PtrListINS_5FieldIdEEEES5_RNS1_INS_9lduMatrix8smootherEEERS3_SA_+0x295)[0x7f255846c4b5]
[MSLab02:31637] [ 9] /home/mslab02/OpenFOAM/OpenFOAM-3.0.x/platforms/linux64GccDPInt32Opt/lib/libOpenFOAM.so(_ZNK4Foam10GAMGSolver5solveERNS_5FieldIdEERKS2_h+0x5fb)[0x7f255847103b]
[MSLab02:31637] [10] /home/mslab02/OpenFOAM/OpenFOAM-3.0.x/platforms/linux64GccDPInt32Opt/lib/libfiniteVolume.so(_ZN4Foam8fvMatrixIdE15solveSegregatedERKNS_10dictionaryE+0x16c)[0x7f255ae5430c]
[MSLab02:31637] [11] pimpleDyMFoam(_ZN4Foam8fvMatrixIdE5solveERKNS_10dictionaryE+0x199)[0x457509]
[MSLab02:31637] [12] pimpleDyMFoam[0x41ed81]
[MSLab02:31637] [13] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xe7)[0x7f255713db97]
[MSLab02:31637] [14] pimpleDyMFoam[0x422449]
[MSLab02:31637] *** End of error message ***
[MSLab02:31634] *** Process received signal ***
[MSLab02:31634] Signal: Floating point exception (8)
[MSLab02:31634] Signal code:  (-6)
[MSLab02:31634] Failing at address: 0x3e800007b92
 at ??:?
[MSLab02:31634] [ 0] /lib/x86_64-linux-gnu/libc.so.6(+0x3ef20)[0x7f2b7f22cf20]
[MSLab02:31634] [ 1] /lib/x86_64-linux-gnu/libc.so.6(gsignal+0xc7)[0x7f2b7f22ce97]
[MSLab02:31634] [ 2] /lib/x86_64-linux-gnu/libc.so.6(+0x3ef20)[0x7f2b7f22cf20]
[MSLab02:31634] [ 3] /home/mslab02/OpenFOAM/OpenFOAM-3.0.x/platforms/linux64GccDPInt32Opt/lib/libOpenFOAM.so(_ZN4Foam17DICPreconditioner15calcReciprocalDERNS_5FieldIdEERKNS_9lduMatrixE+0x85)[0x7f2b80529cd5]
[MSLab02:31634] [ 4] /home/mslab02/OpenFOAM/OpenFOAM-3.0.x/platforms/linux64GccDPInt32Opt/lib/libOpenFOAM.so(_ZN4Foam11DICSmootherC1ERKNS_4wordERKNS_9lduMatrixERKNS_10FieldFieldINS_5FieldEdEESB_RKNS_8UPtrListIKNS_17lduInterfaceFieldEEE+0x12c)[0x7f2b8052667c]
[MSLab02:31634] [ 5] /home/mslab02/OpenFOAM/OpenFOAM-3.0.x/platforms/linux64GccDPInt32Opt/lib/libOpenFOAM.so(_ZN4Foam22DICGaussSeidelSmootherC1ERKNS_4wordERKNS_9lduMatrixERKNS_10FieldFieldINS_5FieldEdEESB_RKNS_8UPtrListIKNS_17lduInterfaceFieldEEE+0x4b)[0x7f2b805277db]
[MSLab02:31634] [ 6] /home/mslab02/OpenFOAM/OpenFOAM-3.0.x/platforms/linux64GccDPInt32Opt/lib/libOpenFOAM.so(_ZN4Foam9lduMatrix8smoother30addsymMatrixConstructorToTableINS_22DICGaussSeidelSmootherEE3NewERKNS_4wordERKS0_RKNS_10FieldFieldINS_5FieldEdEESE_RKNS_8UPtrListIKNS_17lduInterfaceFieldEEE+0x48)[0x7f2b80527aa8]
[MSLab02:31634] [ 7] /home/mslab02/OpenFOAM/OpenFOAM-3.0.x/platforms/linux64GccDPInt32Opt/lib/libOpenFOAM.so(_ZN4Foam9lduMatrix8smoother3NewERKNS_4wordERKS0_RKNS_10FieldFieldINS_5FieldEdEESB_RKNS_8UPtrListIKNS_17lduInterfaceFieldEEERKNS_10dictionaryE+0x237)[0x7f2b80517877]
[MSLab02:31634] [ 8] /home/mslab02/OpenFOAM/OpenFOAM-3.0.x/platforms/linux64GccDPInt32Opt/lib/libOpenFOAM.so(_ZNK4Foam10GAMGSolver10initVcycleERNS_7PtrListINS_5FieldIdEEEES5_RNS1_INS_9lduMatrix8smootherEEERS3_SA_+0x295)[0x7f2b8053e4b5]
[MSLab02:31634] [ 9] /home/mslab02/OpenFOAM/OpenFOAM-3.0.x/platforms/linux64GccDPInt32Opt/lib/libOpenFOAM.so(_ZNK4Foam10GAMGSolver5solveERNS_5FieldIdEERKS2_h+0x5fb)[0x7f2b8054303b]
[MSLab02:31634] [10] /home/mslab02/OpenFOAM/OpenFOAM-3.0.x/platforms/linux64GccDPInt32Opt/lib/libfiniteVolume.so(_ZN4Foam8fvMatrixIdE15solveSegregatedERKNS_10dictionaryE+0x16c)[0x7f2b82f2630c]
[MSLab02:31634] [11] pimpleDyMFoam(_ZN4Foam8fvMatrixIdE5solveERKNS_10dictionaryE+0x199)[0x457509]
[MSLab02:31634] [12] pimpleDyMFoam[0x41ed81]
[MSLab02:31634] [13] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xe7)[0x7f2b7f20fb97]
[MSLab02:31634] [14] pimpleDyMFoam[0x422449]
[MSLab02:31634] *** End of error message ***
--------------------------------------------------------------------------
mpirun noticed that process rank 0 with PID 0 on node MSLab02 exited on signal 8 (Floating point exception).
--------------------------------------------------------------------------

Can anyone tell me how come it is happening, and what additional changes are required to overcome the same.

Thanks in advance.

[rahulksoni]

I have tried many alternatives to handle the issue but to no luck.
At the end, the guess zeroes down on the meshing quality because even a single extremely small cell among millions of cells can cause such problem.

As per my understanding snappyHexMesh attempts to create hex dominated mesh. However, it also utilizes prisms, wedges, pyramids, tet wedges, tetrahedral, polyhedra shaped meshes to attain proper resolution of the small, closed, curved, intricate area which I have near the stirred curved boundaries. The checkMesh results is posted below which lists the distribution of differently shaped meshes:

/*---------------------------------------------------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  3.0.x                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
Build  : 3.0.x-ac3f6c67e02f
Exec   : checkMesh
Date   : Jan 02 2019
Time   : 17:35:36
Host   : "MSLab02"
PID    : 13943
Case   : /media/mslab02/Elements/CFD/StirredMill/OpenFOAM/V11_V10_originalStirredMillRPM1000/V11_V10_originalStirredMillRPM1000
nProcs : 1
sigFpe : Enabling floating point exception trapping (FOAM_SIGFPE).
fileModificationChecking : Monitoring run-time modified files using timeStampMaster
allowSystemOperations : Allowing user-supplied system call operations

/ * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
Create time

Create polyMesh for time = 0

Time = 0

Mesh stats
    points:           680348
    faces:            1824611
    internal faces:   1704405
    cells:            577544
    faces per cell:   6.11038
    boundary patches: 8
    point zones:      0
    face zones:       1
    cell zones:       1

Overall number of cells of each type:
    hexahedra:     504421
    prisms:        22308
    wedges:        0
    pyramids:      0
    tet wedges:    606
    tetrahedra:    4
    polyhedra:     50205
    Breakdown of polyhedra by number of faces:
        faces   number of cells
            4   8241
            5   6425
            6   11229
            7   359
            8   411
            9   13976
           10   49
           11   490
           12   5914
           13   16
           14   15
           15   2748
           18   332

Checking topology...
    Boundary definition OK.
    Cell to face addressing OK.
    Point usage OK.
    Upper triangular ordering OK.
    Face vertices OK.
   *Number of regions: 2
    The mesh has multiple regions which are not connected by any face.
  <<Writing region information to "0/cellToRegion"
  <<Writing region 0 with 488408 cells to cellSet region0
  <<Writing region 1 with 89136 cells to cellSet region1

Checking patch topology for multiply connected surfaces...
                   Patch    Faces   Points                  Surface topology
                   walls      564      616  ok (non-closed singly connected)
           outerCylinder     3908     4733  ok (non-closed singly connected)
            propellerTip    64110    74620  ok (non-closed singly connected)
          propellerStem1      216      308  ok (non-closed singly connected)
          propellerStem2      188      308  ok (non-closed singly connected)
          propellerStem3      248      280  ok (non-closed singly connected)
                    AMI1    25292    25280  ok (non-closed singly connected)
                    AMI2    25680    25773  ok (non-closed singly connected)

Checking geometry...
    Overall domain bounding box (-0.0999999 0 -0.0999997) (0.1 0.18 0.0999998)
    Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
    Mesh has 3 solution (non-empty) directions (1 1 1)
    Boundary openness (9.89662e-18 -5.25118e-17 -1.78104e-17) OK.
    Max cell openness = 3.81187e-16 OK.
    Max aspect ratio = 12.3469 OK.
    Minimum face area = 5.84363e-08. Maximum face area = 0.000118134.  Face area magnitudes OK.
    Min volume = 5.26873e-11. Max volume = 7.32226e-07.  Total volume = 0.00557452.  Cell volumes OK.
    Mesh non-orthogonality Max: 64.9912 average: 10.4571
    Non-orthogonality check OK.
    Face pyramids OK.
 ***Max skewness = 4.15153, 7 highly skew faces detected which may impair the quality of the results
  <<Writing 7 skew faces to set skewFaces
    Coupled point location match (average 0) OK.

Failed 1 mesh checks.

End

I checked snappyHexMeshDict and found that the minVol 1e-13;
I believe this is the limit of smallest cell volume. I changed it to minVol 1e-10;, and obtained following checkMesh results, where one can see the increased dominance of hex meshes and decrease in the number of prisms.

/*---------------------------------------------------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  3.0.x                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
Build  : 3.0.x-ac3f6c67e02f
Exec   : checkMesh
Date   : Jan 02 2019
Time   : 17:35:36
Host   : "MSLab02"
PID    : 13943
Case   : /media/mslab02/Elements/CFD/StirredMill/OpenFOAM/V11_V10_originalStirredMillRPM1000/V11_V10_originalStirredMillRPM1000
nProcs : 1
sigFpe : Enabling floating point exception trapping (FOAM_SIGFPE).
fileModificationChecking : Monitoring run-time modified files using timeStampMaster
allowSystemOperations : Allowing user-supplied system call operations

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
Create time

--> FOAM Warning : 
    From function checkMesh
    in file db/Time/timeSelector.C at line 270
    No time specified or available, selecting 'constant'
Create polyMesh for time = constant

Time = constant

Mesh stats
    points:           719644
    faces:            1873121
    internal faces:   1704405
    cells:            577544
    faces per cell:   6.19438
    boundary patches: 8
    point zones:      0
    face zones:       1
    cell zones:       1

Overall number of cells of each type:
    hexahedra:     541868
    prisms:        40
    wedges:        0
    pyramids:      0
    tet wedges:    0
    tetrahedra:    0
    polyhedra:     35636
    Breakdown of polyhedra by number of faces:
        faces   number of cells
            5   32
            6   11258
            7   8
            8   168
            9   14341
           10   4
           11   472
           12   6202
           15   2811
           18   340

Checking topology...
    Boundary definition OK.
    Cell to face addressing OK.
    Point usage OK.
    Upper triangular ordering OK.
    Face vertices OK.
   *Number of regions: 2
    The mesh has multiple regions which are not connected by any face.
  <<Writing region information to "constant/cellToRegion"
  <<Writing region 0 with 488408 cells to cellSet region0
  <<Writing region 1 with 89136 cells to cellSet region1

Checking patch topology for multiply connected surfaces...
                   Patch    Faces   Points                  Surface topology
                   walls      564      628  ok (non-closed singly connected)
      innerCylinderSmall    31980    32008  ok (non-closed singly connected)
    innerCylinderSmall_slave    31980    32008  ok (non-closed singly connected)
           outerCylinder     4036     4833  ok (non-closed singly connected)
            propellerTip    99192   100561  ok (non-closed singly connected)
          propellerStem1      364      444  ok (non-closed singly connected)
          propellerStem2      240      388  ok (non-closed singly connected)
          propellerStem3      360      400  ok (non-closed singly connected)

Checking geometry...
    Overall domain bounding box (-0.0999992 4.01721e-07 -0.0999992) (0.0999992 0.18 0.0999992)
    Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
    Mesh has 3 solution (non-empty) directions (1 1 1)
    Boundary openness (1.36126e-17 -2.40842e-16 -4.89655e-18) OK.
    Max cell openness = 3.81639e-16 OK.
    Max aspect ratio = 2.60666 OK.
    Minimum face area = 7.10589e-07. Maximum face area = 0.000117019.  Face area magnitudes OK.
    Min volume = 7.83314e-10. Max volume = 7.66753e-07.  Total volume = 0.00551937.  Cell volumes OK.
    Mesh non-orthogonality Max: 42.1181 average: 7.5586
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 1.28544 OK.
    Coupled point location match (average 0) OK.

Mesh OK.

End

One can see that the minVol obtained by the cells is 7.83314e-10.
Now, my simulation works fine.
I further tried to change the minVol (in snappyHexMeshDict) to something like 1E-8 but then even the attained minVol was of the order 1E-10; probably that is the requirement of geometry to properly resolve the curved, intricate areas.