[DashaSh]

Hello everyone,

Can someone tell me how to turn off the equations for the momentum for "foamMultiRun"?


I calculated the pre-initiated field of velocities and pressures. Now I want to calculate my case with only heat transfer. I turned off the flow equations in fvSolution. When I start running the case, the velocity are not calculated in residuals, but the velocity field still changes.

Please someone tell me what could be the problem?

fvSolution:

PIMPLE
{
    flow off;
    momentumPredictor off;
    nOuterCorrectors 30;
    nCorrectors     1;
    nNonOrthogonalCorrectors 0; 
...

physicalProperties:

thermoType
{
    type            heRhoThermo;
    mixture         pureMixture;
    transport       const;
    thermo          eConst;
    equationOfState rPolynomial;
    specie          specie;
    energy          sensibleInternalEnergy;
}

mixture
{
    specie
    {
        molWeight       18.015;
    }
    equationOfState
    {
        rho0            1000;
        T0              278;
        //beta            2e-04;
        C (0.001278 -2.1055e-06 3.9689e-09 4.3772e-13 -2.0225e-16);
    }

from log file:

wedge0_rotated diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
wedge0_rotated DILUPBiCGStab:  Solving for e, Initial residual = 0.000680102566017, Final residual = 5.34837357105e-05, No Iterations 1
wedge0_rotated DICPCG:  Solving for p_rgh, Initial residual = 0.00296039703522, Final residual = 9.69628888453e-09, No Iterations 595
wedge0_rotated diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
wedge0_rotated time step continuity errors : sum local = 1.40253056235e-10, global = -7.49192173107e-13, cumulative = -8.68144446708e-09

[Mid_Night]

Hi, make a minIter 0 for fluid in fvSolution, except for pressure (but I'm not sure)

[DashaSh]

After testing different configurations, I would like to share my observations and conclusions:

The problem was in the equations of state. I considered a compressible fluid in my case, which is why the velocity field could not remain the same as in the case of an incompressible fluid.

So I came to the conclusion that we cannot simultaneously consider a compressible fluid and an unchanging field of velocities and pressures.

[thiagopl]

Hi Dasha,

I don't know wether the compressible fluid is really the problem. In OF10 I run multi region cases with fluid as a perfect gas and flow off; withou any problem.
Now, in OF12, I have the same problem as yours and can't find a solution.
I am running a simple multi region case and want to turn off the solution of the momentum equations. To do this, my fvSolution is as bellow (I am using a template file so I have all of the solvers in there, but I don't need most of them).

solvers
{
    "(rho|rhoFinal)"
    {
        solver          PCG
        preconditioner  DIC;
        tolerance       1e-7;
        relTol          0;
    }

    p_rgh
    {
        solver           GAMG;
        tolerance        1e-7;
        relTol           0.01;

        smoother         GaussSeidel;
        maxIter          100;
    }

    "(U|h|e|k|omega|epsilon)"
    {
        solver          PBiCGStab;
        preconditioner  DILU;
        tolerance       1e-6;
        relTol          0.1;
    }

    G
    {
        $p_rgh;
        tolerance       1e-5;
        relTol          0.1;
    }

    p_rghFinal
    {
        $p_rgh;
      relTol         0;  // for transient cases
    }

    "(U|h|e|k|omega|epsilon)Final"
    {
        $U;
      relTol         0;  // for transient cases
    }

    GFinal
    {
        $G;
      relTol         0;  // for transient cases
    }
}

PIMPLE
{
    flow   off;
    momentumPredictor off;
    
    nCorrectors     2;//1;          // typically set to 2 for transient
    nNonOrthogonalCorrectors 1;//0; // typically set to 1 for transient

//  Reference values for closed domains
    pRefCell        0;
    pRefValue       1e5;

}

// For transient cases, use
 relaxationFactors { equations { ".*" 1; } }

My fluid region is filled with an incompressible fluid as set in fluid/physicalProperties:

thermoType
{
    type            heRhoThermo;
    mixture         pureMixture;
    transport       const;
    thermo          hConst;
    equationOfState rhoConst;
    specie          specie;
    energy          sensibleEnthalpy;
}

mixture
{
    specie
    {
        nMoles      1;
        molWeight   28.9;       // [kg/kmol]
    }
    thermodynamics
    {
        Cp          1005;       // [J/kg/K]
        hf          0;
    }
    transport
    {
        mu          1.8e-05;    // [kg/m/s]
        Pr          0.7;
    }
    equationOfState
    {
    	rho	1.205;
    }
}

Despite the configuration above, the momentum equations are still being solved:

Starting time loop

solid Diffusion Number mean: 0.71902655 max: 0.94816688
      Time = 1s
      
fluid DILUPBiCGStab:  Solving for h, Initial residual = 1, Final residual = 0.091275176, No Iterations 2
solid DICPCG:  Solving for e, Initial residual = 0.91986188, Final residual = 2.683097e-08, No Iterations 4
fluid GAMG:  Solving for p_rgh, Initial residual = 1, Final residual = 2.1909564e-06, No Iterations 1
fluid GAMG:  Solving for p_rgh, Initial residual = 0.66776673, Final residual = 0.0026255464, No Iterations 4
fluid time step continuity errors : sum local = 0.015898823, global = 3.2104902e-18
fluid GAMG:  Solving for p_rgh, Initial residual = 0.56163081, Final residual = 0.0042177458, No Iterations 4
fluid GAMG:  Solving for p_rgh, Initial residual = 0.0047033722, Final residual = 2.6678637e-05, No Iterations 5
fluid time step continuity errors : sum local = 1.4260071e-06, global = -2.154346e-20, cumulative = -2.154346e-20
      ExecutionTime = 0.094377 s  ClockTime = 0 s

So my question is the same, how to turn off the momentum equations solution on a foamMutliRun case?
The case is attached and it runs with the comand in terminal: bash Allrun

[Tobermory]

Not sure why your pressure is being updated ... I have a CHT setup and have turned off flow and momentumPredictor in system/gas/fvSolution and it only solves for rho and h in my fluid, and e in my solid. Differences in my setup:
- I have perfectGas for the fluid instead of rhoConst in constant/gas/physicalProperties
- I have left nCorrectors and nNonOrthogonalCorrectors undefined in system/gas/fvSolution, i.e. default values instead of your specified 2 and 1 (which perhaps forces updates of the p_rgh field?)

Hope that helps.