[Skaiwalker]

Dear forum,

I want to simulate laminar jets of nitrogen pointed on a hot surface through multiple inlet variations. The geometry is shown in the following picture. The blue dots are inlets, the refinement boxes on the sides of the domain are outlets. Its a plain simple box with some inlet/outlet extension and symmetry on the side missing the outlet refinement.

furnaceAtm_measurements.jpg

I started with simpleFoam as a first indicator and want to model buoyancy effects later on. From 22M cells on the results look promising physically. Before, the flow is all over the place, as you can see in the following 2 screenshots. The Threshold of the highlighted cells reaches from U=0.1 to max U

4.3M cells: Uglyph_4.3MCells.jpg 40M cells: Uglyph_40MCells.jpg


I compare the volume average velocities as an indicator of mesh convergence but further refinement does not lead to converging results, I can't even see a trend in the attached graph, especially for Ux. After gradual refinement I ended up with a 40M cell behemoth with a cell length of 1 mm in the coarse volume, up to 0.06 mm in the refined areas and 10 very thin growing layers. Detailed screenshots and a case without mesh are uploaded to oneDrive, the checkMesh results are attached at the end of the post.

volAvgU.jpg

Question: Am I refining the right places in the mesh and what can I do to achieve mesh convergence? My machine is on it's limit with 40M cells


CheckMesh:

/*---------------------------------------------------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  8
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/
Build  : 8-1c9b5879390b
Exec   : checkMesh -allGeometry -allTopology
Date   : Jun 29 2021
Time   : 11:11:08
Host   : "ipl-pc271"
PID    : 4074
I/O    : uncollated
Case   : /home/ksalscheider/projects/pruefstand_mb125/run/V1/comfortHotRoom_40M_sizeBoxes_layers_buoyantSimpleFoam_simpleFoamInit
nProcs : 1
sigFpe : Enabling floating point exception trapping (FOAM_SIGFPE).
fileModificationChecking : Monitoring run-time modified files using timeStampMaster (fileModificationSkew 10)
allowSystemOperations : Allowing user-supplied system call operations

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

Create polyMesh for time = 0

Enabling all (cell, face, edge, point) topology checks.

Enabling all geometry checks.

Time = 0

Mesh stats
    points:           30043880
    faces:            108203165
    internal faces:   107332983
    cells:            39829127
    faces per cell:   5.41152
    boundary patches: 19
    point zones:      0
    face zones:       1
    cell zones:       2

Overall number of cells of each type:
    hexahedra:     26938846
    prisms:        554311
    wedges:        0
    pyramids:      1787637
    tet wedges:    0
    tetrahedra:    10548333
    polyhedra:     0

Checking topology...
    Boundary definition OK.
    Cell to face addressing OK.
    Point usage OK.
    Upper triangular ordering OK.
    Face vertices OK.
    Topological cell zip-up check OK.
    Face-face connectivity OK.
    Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces...
    Patch               Faces    Points   Surface topology                   Bounding box
    symmetrie           62190    62887    ok (non-closed singly connected)  
    tiegelwand          127818   129099   ok (non-closed singly connected) 
    schmelzbadoberflaeche292649   293417   ok (non-closed singly connected) 
    tiegeldeckel        288994   289301   ok (non-closed singly connected)  
    outlets             62500    65078    ok (non-closed singly connected)  
    inlet_A1            922      934      ok (non-closed singly connected)   
    inlet_A2            946      964      ok (non-closed singly connected)   
    inlet_A5            904      923      ok (non-closed singly connected)   
    inlet_B1            957      974      ok (non-closed singly connected)   
    inlet_C1            920      938      ok (non-closed singly connected)   
    inlet_C2            930      944      ok (non-closed singly connected)   
    inlet_C3            915      927      ok (non-closed singly connected)   
    inlet_C4            907      922      ok (non-closed singly connected)  
    inlet_C5            944      966      ok (non-closed singly connected) 
    inlet_C6            913      933      ok (non-closed singly connected) 
    inlet_C7            919      938      ok (non-closed singly connected) 
    inlet_C8            918      935      ok (non-closed singly connected)   
    inletChannels       17136    18144    ok (non-closed singly connected)
    outletChannels      7800     10412    ok (non-closed singly connected)

Checking geometry...
    Overall domain bounding box (-0.301 3.97904e-16 -0.08) (0.301 0.301 0.001)
    Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
    Mesh has 3 solution (non-empty) directions (1 1 1)
    Boundary openness (6.57636e-16 6.98591e-16 4.23246e-15) OK.
    Max cell openness = 4.70579e-16 OK.
    Max aspect ratio = 120.444 OK.
    Minimum face area = 3.04033e-10. Maximum face area = 2.33772e-06.  Face area magnitudes OK.
    Min volume = 2.98042e-15. Max volume = 1.04958e-09.  Total volume = 0.01441.  Cell volumes OK.
    Mesh non-orthogonality Max: 59.9915 average: 10.9556
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 1.35357 OK.
    Coupled point location match (average 0) OK.
    Face tets OK.
    Min/max edge length = 1.86863e-06 0.00183555 OK.
    All angles in faces OK.
    Face flatness (1 = flat, 0 = butterfly) : min = 0.951441  average = 0.999999
    All face flatness OK.
    Cell determinant (wellposedness) : minimum: 2.47088e-06 average: 5.07848
 ***Cells with small determinant (< 0.001) found, number of cells: 1464477
  <<Writing 1464477 under-determined cells to set underdeterminedCells
    Concave cell check OK.
    Face interpolation weight : minimum: 0.0624713 average: 0.471401
    Face interpolation weight check OK.
    Face volume ratio : minimum: 0.066634 average: 0.898815
    Face volume ratio check OK.

Failed 1 mesh checks.

End