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Diverging Temperature in LES - which settings to adjust?

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Old   February 23, 2016, 23:14
Default Diverging Temperature in LES - which settings to adjust?
Join Date: Aug 2015
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knuckles is on a distinguished road
I'm running LES of a turbulent jet using ~1.6 million cells and a Courant Number of 0.3. My solver is customized, but all of the non-standard features are turned off and it should be behaving identically to reactingFoam with all reactions turned off. At some point, an instability arises: at first, I get a few warnings that T is outside of the allowable range (300-5000 K) - say 5100 K - but then these warnings get more frequent and more problematic, until there are thousands at each time step and the associated temperatures range from -1e16 to +1e16.

My best guess for what's going on is that I've failed to appropriately model the pressure-momentum coupling, and that I need to add more pimple loops - is this the correct fix? I have seen an article [] which suggests, among other things:
  • Set nOuterCorrectors up to a very high number (~ 50 to 200) and control your pimple loop with the residual control
  • Set nCorrectors to a small number (1 to 3; you have to play around)
...however, I've never seen this first suggestion implemented in a tutorial other than the one described at the link above.

My question: What settings should I be changing to avoid this instability?

For reference:

The output of checkMesh:
Mesh stats
    points:           1617892
    faces:            4824873
    internal faces:   4797927
    cells:            1603800
    faces per cell:   6
    boundary patches: 5
    point zones:      0
    face zones:       0
    cell zones:       0

Overall number of cells of each type:
    hexahedra:     1603800
    prisms:        0
    wedges:        0
    pyramids:      0
    tet wedges:    0
    tetrahedra:    0
    polyhedra:     0

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                  
    JET                 405      424      ok (non-closed singly connected)  
    PILOT               864      900      ok (non-closed singly connected)  
    COFLOW              1404     1440     ok (non-closed singly connected)  
    OUTERRADIUS         21600    21636    ok (non-closed singly connected)  
    OUTLET              2673     2692     ok (non-closed singly connected)  

Checking geometry...
    Overall domain bounding box (-0.07172601826 -0.07172601826 0) (0.07172601826 0.07172601826 0.36)
    Mesh (non-empty, non-wedge) directions (1 1 1)
    Mesh (non-empty) directions (1 1 1)
    Boundary openness (2.5360889850782e-16 2.502408869494276e-16 3.295433281148142e-16) OK.
    Max cell openness = 4.165398281849697e-16 OK.
    Max aspect ratio = 22.5683629471026 OK.
    Minimum face area = 5.055728864375342e-08. Maximum face area = 3.708057695313814e-05.  Face area magnitudes OK.
    Min volume = 1.872805105800212e-11. Max volume = 4.104974063197774e-08.  Total volume = 0.003402726340535457.  Cell volumes OK.
    Mesh non-orthogonality Max: 22.23980401213051 average: 2.729797707905458
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 0.5165905340833714 OK.
    Coupled point location match (average 0) OK.

Mesh OK.
My system/fvSchemes

    default         backward;

    default         Gauss linear;

    div(phi,rho)    Gauss limitedLinear phi 1;
    default         Gauss limitedLinear 1;
    div(phi,U)      Gauss limitedLinearV 1;
    div(phi,Yi_h)   Gauss multivariateSelection 
        CO2               limitedLinear01 1; 
        H2O               limitedLinear01 1;
        NO                limitedLinear01 1;
        N2                limitedLinear01 1;
        h                 limitedLinear   1;
    div((muEff*dev2(T(grad(U))))) Gauss linear;

    default         Gauss linear corrected;

    default         linear;

    default         corrected;

    default         no;
My system/fvsolution:
        relTol          0; 
        solver          smoothSolver; 
        smoother        symGaussSeidel; 
        tolerance       1e-06; 
        relTol          0.01; 
        relTol          0; 
    momentumPredictor yes; 
    nOuterCorrectors  2; 
    nCorrectors     3; 
    nNonOrthogonalCorrectors 2; 
    turbOnFinalIterOnly false; 
        ".*"    1; 
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Old   March 7, 2016, 15:32
Join Date: Aug 2015
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I believe I found the problem. I had a turbulentInlet BC and the magnitude of the fluctuations was far too large - presumably this caused this instability. For reference, a fluctuationScale of 0.1 or larger is very big.
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