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Age of air with function object

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Old   April 14, 2018, 13:07
Default Age of air with function object
Ruggiero Guida
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I have added a function object to calculate the Age Of Air in OF4.1. SimpleFoam converges, but I have some doubt about the interpretation of the results.

I have based the implementation on this thread

Mean Age of Air

In my controlDict I have added the following function

    type    scalarTransport;
    functionObjectLibs ("");
    enabled true;
    writeControl outputTime;
    log yes;
    nCorr 1;

    field AoA;
    active          true;
    autoSchemes     false;
    resetOnStartUp false;
    DT              1e-5;

            type            scalarSemiImplicitSource;
            active          true;
                selectionMode all;
                volumeMode  specific;
                    AoA       (1 0);
I have then added the following boundary condition

dimensions [ 0 0 1 0 0 0 0 ];

internalField uniform 0.0;   

    type fixedValue;
    value uniform 0;
    type zeroGradient;
Modified fvSchemes and fvSolution accordingly with

div(phi,AoA) bounded Gauss upwind;

        solver           smoothSolver;
        smoother         GaussSeidel;
        tolerance        1e-08;
        relTol           0.1;
        nsweep                   1;
The solution converges, but I am not really sure I get what it means. My understanding is:
  • We inject some kind of tracer at each point of the domain
  • We assign uniform zero as BC
  • The value of AoA tells us how long, in average, it will take for the air in that point to be replaced by new air coming from the boundary (outside)
  • This is why we assign uniform 0 at the boundary

Is this correct?
What does IncrementTime actually do?
Why AoA has unit of Time?
Why we inject 1 of tracer?
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Old   February 7, 2021, 14:49
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It took me three years to reflect on these questions (kidding)

(maybe not)

Age of Air Function Object
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