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Passive Scalar Out of Bounds Channel

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Old   August 22, 2017, 17:22
Default Passive Scalar Out of Bounds Channel
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Hello to all,
I'm solving the flow in a very simple geometry: the well known Tjunction channel. It is a microfluids device so the dimensions are of the order of 10^(-6). The flow is completely laminar due to the very low Re number (Re=100). The channel is characterized by two inlets and one outlet. I linked an image to be more clear.
My flow is single phase, water at ambient temperature. Now, after the calculation of the velocity and pressure field with simpleFoam, i run a simulation to calculate the passive scalar (DT=3*10^(-10)). At one inlet i imposed a T=0 while at the other T=1 and then i run scalarTransportFoam. In this manner i can observe how the two flows mix in the outlet channel. The big problem is that my scalar goes out of bound, this means i find value larger 1 and it shouldn't happen. I tried to fix the problem using different schemes for the divergence as suggested in other threads but nothing, the problem is always there.
Is there someone who have experience in this type of problems?

I link also the two cases.
Thanks for help.


Best Regards,
Roberto
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File Type: gz Scalar.tar.gz (1.8 KB, 3 views)
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Old   August 23, 2017, 02:45
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Check your mesh.
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Old   August 23, 2017, 04:24
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Hi akidess, first thank you for your reply.

Quote:
Originally Posted by akidess View Post
Check your mesh.
What do you mean? Sorry, i don't understand.
Here there is my output after running checkMesh


Code:
/*---------------------------------------------------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v1612+                                |
|   \\  /    A nd           | Web:      www.OpenFOAM.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
Build  : v1612+
Exec   : checkMesh
Date   : Aug 23 2017
Time   : 10:19:27
Host   : "Nitro"
PID    : 4231
Case   : /home/roby/Scrivania/0.4/Direct
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

Time = 0

Mesh stats
    points:           306516
    faces:            863850
    internal faces:   810150
    cells:            279000
    faces per cell:   6
    boundary patches: 5
    point zones:      0
    face zones:       0
    cell zones:       0

Overall number of cells of each type:
    hexahedra:     279000
    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                  
    walls               45900    46330    ok (non-closed singly connected)  
    inlet1              300      336      ok (non-closed singly connected)  
    inlet2              300      336      ok (non-closed singly connected)  
    movable             6600     6951     ok (non-closed singly connected)  
    outlet              600      651      ok (non-closed singly connected)  

Checking geometry...
    Overall domain bounding box (-0.00015 -0.00165 0) (0.003 0.00165 0.0002)
    Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
    Mesh has 3 solution (non-empty) directions (1 1 1)
    Boundary openness (-6.91724e-18 1.96638e-18 2.57098e-17) OK.
    Max cell openness = 1.29247e-16 OK.
    Max aspect ratio = 1 OK.
    Minimum face area = 1e-10. Maximum face area = 1e-10.  Face area magnitudes OK.
    Min volume = 1e-15. Max volume = 1e-15.  Total volume = 2.79e-10.  Cell volumes OK.
    Mesh non-orthogonality Max: 0 average: 0
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 3.4169e-13 OK.
    Coupled point location match (average 0) OK.

Mesh OK.

End
It seems ok to me. Is there something i forgot?


Best Regards,
Roberto
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Old   August 23, 2017, 04:41
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Hello Roberto,
did you check your fvSchemes settings? Using Gauss limitedLinear 1; for the divergence scheme of the passive scalar usually works fine for me.

Last edited by RobertHB; August 23, 2017 at 05:57.
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Old   August 23, 2017, 08:51
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Quote:
Originally Posted by RobertHB View Post
Hello Roberto,
did you check your fvSchemes settings? Using Gauss limitedLinear 1; for the divergence scheme of the passive scalar usually works fine for me.
Hello, Robert.
I tried the "Gauss limitedLinear01 1" scheme for the divergence but nothing, the solution continues to be out of bounds
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Old   August 25, 2017, 03:31
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Little update
I noticed few days ago something strange: of you not copy the phi file in the 0 folder scalarTransportFoam produces a phi file which is different from that produced by simpleFoam. This is very strange. Using the phi file produced by simpleFoam the solution improves but not enough.
Why this difference?


Best Regards,
Roberto
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