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-   -   Climbing inlet pressure with simpleFoam and directMappedPatches (http://www.cfd-online.com/Forums/openfoam-solving/93576-climbing-inlet-pressure-simplefoam-directmappedpatches.html)

chegdan October 19, 2011 13:14

Climbing inlet pressure with simpleFoam and directMappedPatches
 
Hello,

I've been racking my brain trying to figure this one out and its stumped me. I'm using a really complicated 3d Mesh over the domain below:

https://dl-web.dropbox.com/get/Publi...png?w=392bfba0

and it has been decomposed in scotch like so:

http://dl.dropbox.com/u/35794017/pro...stribution.png

All works fine (no errors) with simpeFoam and directMapped patches and I get convergence plots looking like

http://dl.dropbox.com/u/35794017/convergeBetter.png

I'm monitoring point values around the domain in various locations and everything just keeps increasing linearly. Nothing seems to be topping off and evening out. On courser meshes, I do get some flattening of values...but im interested in the fine mesh. I am looking at changing my pRefCell to someplace different...but Im not sure if that will help. I also tried to use cyclic boundary conditions and make a simpleChannelFoam hybrid of channelFoam and simpleFoam with no luck on convergence (in the channel solver, i get pretty crazy gradP within 10 iterations). Any thoughts? Could it be my discretization using linearUpwind? Sorry for the large pictures in the post. Patch summary is :

Code:

Time = 2001

Valid fields:
    volScalarField        nut
    volVectorField        U
    volScalarField        k
    volScalarField        p
    volScalarField        epsilon

wall: particles
    scalar                nut                calculated
    scalar                k                zeroGradient
    scalar                p                zeroGradient
    scalar                epsilon                zeroGradient
    vector                U                fixedValue

wall: tube
    scalar                nut                calculated
    scalar                k                zeroGradient
    scalar                p                zeroGradient
    scalar                epsilon                zeroGradient
    vector                U                fixedValue

patch: outlet
    scalar                nut                zeroGradient
    scalar                k                zeroGradient
    scalar                p                fixedValue
    scalar                epsilon                zeroGradient
    vector                U                zeroGradient

symmetryPlane: zyplane
    scalar                nut                symmetryPlane
    scalar                k                symmetryPlane
    scalar                p                symmetryPlane
    scalar                epsilon                symmetryPlane
    vector                U                symmetryPlane

symmetryPlane: zxplane
    scalar                nut                symmetryPlane
    scalar                k                symmetryPlane
    scalar                p                symmetryPlane
    scalar                epsilon                symmetryPlane
    vector                U                symmetryPlane

directMappedPatch: inlet
    scalar                nut                zeroGradient
    scalar                k                directMapped
    scalar                p                zeroGradient
    scalar                epsilon                directMapped
    vector                U                directMapped

End


chegdan January 2, 2012 20:35

figured out a solution to my problem
 
Just thought I would provide an answer in case anyone else is looking for an answer. I ended up using an inletOutlet condition for velocity at the exit with

Code:

    outlet
    {
        type            inletOutlet;
        inletValue      uniform ( 1e-20 1e-20 1e-20 );
        value          uniform ( 0 0 1 );
    }

and I used a fixedMeanValue boundary condition for pressure that can be found at (http://www.cfd-online.com/Forums/ope...condition.html). The condition can be used with

Code:

    outlet
    {
        type            fixedMeanValue;
        value          uniform 1;
        meanValue      1e-20;
    }

using this with limited schemes and celllimited gradient schemes on a polyhedral mesh....the rise in pressure eventually leveled out. I monitored the pressure drop between the inlet and outlet and once that was constant, 10 probe points were constant, and the residuals dropped to a level lower than 1e-4 it was an acceptable answer.


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