[angatri_14]

Dear foamers,
I'm working on a Blade-Vortex incidence simulation (LES). As usual, I need a reference situation to compare BVI effects which obviously is the flow around the chosen airfoil (SD7003). The case is assumed incompressible, with Re=60000.

My mesh is all generated using blockMesh, with y+~0.3. Using checkMesh utility gives me the following result (I think it is a good mesh):

/*---------------------------------------------------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v1912 |
| \\ / A nd | Website: www.openfoam.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
Build : _f3950763fe-20191219 OPENFOAM=1912
Arch : "LSB;label=32;scalar=64"
Exec : checkMesh -constant
Date : Jul 15 2020
Time : 14:20:50
Host : DESKTOP-2A2DNRL
PID : 618
I/O : uncollated
Case : /mnt/c/Users/usuario/Desktop/SD7003_smag_2
nProcs : 1
trapFpe: Floating point exception trapping enabled (FOAM_SIGFPE).
fileModificationChecking : Monitoring run-time modified files using timeStampMaster (fileModificationSkew 10)
allowSystemOperations : Allowing user-supplied system call operations

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

Create mesh for time = constant

Time = constant

Mesh stats
points: 1946320
faces: 5541520
internal faces: 5254120
cells: 1798000
faces per cell: 6.00425
boundary patches: 5
point zones: 1
face zones: 3
cell zones: 0

Overall number of cells of each type:
hexahedra: 1790340
prisms: 0
wedges: 0
pyramids: 0
tet wedges: 0
tetrahedra: 0
polyhedra: 7660
Breakdown of polyhedra by number of faces:
faces number of cells
6 750
7 6180
8 730

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
inlet 7400 8151 ok (non-closed singly connected)
outlet 3600 3971 ok (non-closed singly connected)
airfoil 10000 10500 ok (non-closed singly connected)
front 133200 134000 ok (non-closed singly connected)
back 133200 134000 ok (non-closed singly connected)

Checking faceZone topology for multiply connected surfaces...
FaceZone Faces Points Surface topology
interface1interface20MasterZone 1200 1341 ok (non-closed singly connected)
interface1interface20SlaveZone 0 0 ok (empty)
interface1interface20CutFaceZone 0 0 ok (empty)

Checking basic cellZone addressing...
No cellZones found.

Checking geometry...
Overall domain bounding box (-5 -6 0) (11 6 0.2)
Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
Mesh has 3 solution (non-empty) directions (1 1 1)
Boundary openness (5.82366e-17 -4.73876e-17 3.48932e-15) OK.
Max cell openness = 4.70497e-15 OK.
Max aspect ratio = 362.993 OK.
Minimum face area = 1.01946e-07. Maximum face area = 0.0351612. Face area magnitudes OK.
Min volume = 1.01946e-09. Max volume = 0.000703225. Total volume = 35.2987. Cell volumes OK.
Mesh non-orthogonality Max: 64.2824 average: 19.7013
Non-orthogonality check OK.
Face pyramids OK.
Max skewness = 0.989044 OK.
Coupled point location match (average 0) OK.

Mesh OK.

End
End

I'm using pimple in piso mode, since I'm interested in small time resolution at the same time it allows control Co number. Problems arrive here: my simulation is too slow in my opinion (After studying how cores I should use for getting optimum speedup) since I'm using 60 cores and mesh has around 1.8 million cells and it spends 16h to reach 2.13 time. But the worse is that coefficients are wrong as shown in pictures attached (also residuals). Lift coefficient could be wrong due to starting vortex, I mean, the flow is not fully developed. However, drag coefficient takes negatives values.

I have tried changing time schemes (crank-Nicholson, backwards and even first order),space schemes, pimple parameters, orthogonal correctors and finally, I have tested a 2D case, but problems remains the same. I did not try to change my mesh because I think is ok...The folder case is also attached. Due to size limitation I'm not able to upload log.pimplefoam file, but I can send it via email.residuals.png

coef_cd.pdf

coef_cl.pdf

mesh_1.jpg

SD7003.zip Any suggestions?

Thanks a lot to all community members, this forum is really useful!
Best regards, Ángel.

[Tobermory]

Just a few quick observations, since I am afraid that I haven't dug into your zip files. If you are after a steady state set of lift & drag coeffs, why not take advantage of the PIMPLE algorithm and run with a much larger time step - ie Co > 1? You'll get to your steady solution far more quickly then.

Other points: OpenFOAM has very little numerical damping cf commercial CFD codes, and so with a fine mesh and a small time step your hi Re solution will probably show instability that may be causing the solver to work hard. Alternatively, are your tolerances too tight? Take a look at the run log output and see what it is doing each time step.

Finally - I am not sure how you are calculating your coeffs, but do keep in mind that the pressure "p" in the incompressible solvers is kinematic pressure, i.e. is actually p/rho. That will affect the values, but of course won't flip the sign on t he drag. It's probably worth just examining the pressure field in paraView and then doing a handcalculation estimate for the coeffs to check that your coeff calculation is doing what you think it should be doing.

Good luck!

[angatri_14]

Dear Tobermory,
First of all, thanks for your reply. I think you are right, for this reference case, I could use PIMPLE. However, when I tried it seems to be slower than PISO due to internal loops, but I will try again.

Talking about tolerance, I have attached fvSolution and fvSchemes files. I increased pressure tolerance in order to reduce residual. I will see pressure distribution in Paraview as you have said.

Thank you so much for your time!

[angatri_14]

fvSchemes code:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v1912                                 |
|   \\  /    A nd           | Website:  www.openfoam.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "system";
    object      fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
    default backward;
}

d2dt2Schemes
{
	
}

gradSchemes
{
    default         Gauss linear;

    grad(nuTilda)   cellLimited Gauss linear 1;
    grad(U)         cellLimited Gauss linear 1;
}

divSchemes
{
    default        Gauss limitedLinear;
    div(phi,U)      Gauss linear;
    div(phi,k)      Gauss limitedLinear 1;
    div(phi,B)      Gauss limitedLinear 1;
    div(B)          Gauss linear;
    div(phi,nuTilda) Gauss limitedLinear 1;
    div((nuEff*dev2(T(grad(U))))) Gauss linear;
}

laplacianSchemes
{
    default         Gauss linear limited  0.33;
}

interpolationSchemes
{
    default         linear;
}

snGradSchemes
{
    default         limited  0.33;
}

wallDist
{
    method meshWave;
}


// ************************************************************************* //

fvSolution code:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v1912                                 |
|   \\  /    A nd           | Website:  www.openfoam.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "system";
    object      fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
    p
    {
        solver          GAMG;
        tolerance       1e-7;
        relTol          0.001;

        smoother        GaussSeidel;


        nCellsInCoarsestLevel 50;
    }

    pFinal
    {
        $p;
        relTol          0;

        // Explicit specify solver for coarse-level correction to override
        // solution tolerance
        coarsestLevelCorr
        {
            solver          PCG;
            preconditioner  DIC;
            relTol          0.001;
        }
    }

    "(U|k|B|nuTilda)"
    {
        solver          smoothSolver;
        smoother        symGaussSeidel;
        tolerance       1e-6;
        relTol          0;
    }

   UFinal
    {
        $U;
        tolerance       1e-05;
        relTol          0;
    }

  kFinal
    {
        $k;
        tolerance       1e-05;
        relTol          0;
    }
}
PIMPLE
{
    nCorrectors     3;
    nOuterCorrectors 1;
    nNonOrthogonalCorrectors 1;


     pRefCell        1001;
     pRefValue       0;
}




 

// ************************************************************************* //