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 Raza Javed June 16, 2019 05:41

p_rgh and time step continuity error

Hello Everyone,

I am using chtMultiRegionSimpleFoam and my OpenFoam version is 4.1.

I have multiple regions in my geometry and one region is the fluid region, and I am modelling turbulent flow in this.

I am a bit confused about that What is p_rgh?

And how to decide boundary conditions for this?

In my case, I have fixed inlet velocity and zeroGradient at the outlet. Pressure in the complete fluid region has calculated boundary condition.

But I am not sure about p_rgh, what boundary conditions to put?

My changeDictionaryDict file is below:

Code:

```boundary {     inlet     {         type            patch;     }     outlet     {         type            patch;     } } T {     internalField  uniform 300;     boundaryField     {         inlet         {             type            fixedValue;             value          \$internalField;                     }         outlet         {             type            zeroGradient;             value          \$internalField;         }         "fluid_to_box"         {             type            compressible::turbulentTemperatureCoupledBaffleMixed;             Tnbr            T;             kappaMethod    fluidThermo;             value          uniform 300;         }     } } U {     internalField  uniform (0 0 0);     boundaryField     {         inlet         {             type            fixedValue;             value          uniform (0 0 -1.33);         }         outlet         {             type            zeroGradient;         }         "fluid_to_box"         {             type            noSlip;         }     } } epsilon {     internalField  uniform 0.01;     boundaryField     {         inlet         {             type            fixedValue;             value          uniform 0.01;         }         outlet         {             type            inletOutlet;             inletValue      uniform 0.01;         }         ".*"         {             type            epsilonWallFunction;             value          uniform 0.01;         }     } } k {     internalField  uniform 0.1;     boundaryField     {         inlet         {             type            inletOutlet;             inletValue      uniform 0.1;         }         outlet         {             type            zeroGradient;             value          uniform 0.1;         }         ".*"         {             type            kqRWallFunction;             value          uniform 0.1;         }     } } p_rgh {     internalField  uniform 0;     boundaryField     {         inlet         {             type            zeroGradient;             value          uniform 0;         }         outlet         {             type            fixedValue;             value          uniform 0;         }         ".*"         {             type            fixedFluxPressure;             value          uniform 0;         }     } } p {     internalField  uniform 0;     boundaryField     {         ".*"         {             type            calculated;             value          uniform 0;         }     } } /*p {     internalField  uniform 0;     boundaryField     {         inlet         {             type            zeroGradient;//fixedValue;             //value          uniform 10;         }         outlet         {             type            fixedValue;             value          uniform 0;         }         "fluid_to_.*"         {             type            zeroGradient;         }     } }*/ alphat {     internalField  uniform 0;     boundaryField     {         inlet         {             type            calculated;//fixedValue;             value          uniform 0;         }         outlet         {             type            calculated;             value          uniform 0;         }         "fluid_to_box"         {             type            compressible::alphatWallFunction;             value          uniform 0;         }         //#includeEtc "caseDicts/setConstraintTypes"     } } nut {     internalField  uniform 0;     boundaryField     {         inlet         {             type            calculated;             value          uniform 0;         }         outlet         {             type            calculated;             value          uniform 0;         }         "fluid_to_box"         {             type            nutkWallFunction;             value          uniform 0;         }         //#includeEtc "caseDicts/setConstraintTypes"     } } // ************************************************************************* //```

When I am running the solver it gives me the following error.

Code:

```--> FOAM FATAL ERROR: Maximum number of iterations exceeded     From function Foam::scalar Foam::species::thermo<Thermo, Type>::T(Foam::scalar, Foam::scalar, Foam::scalar, Foam::scalar (Foam::species::thermo<Thermo, Type>::*)(Foam::scalar, Foam::scalar) const, Foam::scalar (Foam::species::thermo<Thermo, Type>::*)(Foam::scalar, Foam::scalar) const, Foam::scalar (Foam::species::thermo<Thermo, Type>::*)(Foam::scalar) const) const [with Thermo = Foam::hConstThermo<Foam::rhoConst<Foam::specie> >; Type = Foam::sensibleEnthalpy; Foam::scalar = double; Foam::species::thermo<Thermo, Type> = Foam::species::thermo<Foam::hConstThermo<Foam::rhoConst<Foam::specie> >, Foam::sensibleEnthalpy>]     in file /home/ubuntu/OpenFOAM/OpenFOAM-4.1/src/thermophysicalModels/specie/lnInclude/thermoI.H at line 66. FOAM aborting #0  Foam::error::printStack(Foam::Ostream&) at ??:? #1  Foam::error::abort() at ??:? #2  Foam::heRhoThermo<Foam::rhoThermo, Foam::pureMixture<Foam::constTransport<Foam::species::thermo<Foam::hConstThermo<Foam::rhoConst<Foam::specie> >, Foam::sensibleEnthalpy> > > >::calculate() at ??:? #3  Foam::heRhoThermo<Foam::rhoThermo, Foam::pureMixture<Foam::constTransport<Foam::species::thermo<Foam::hConstThermo<Foam::rhoConst<Foam::specie> >, Foam::sensibleEnthalpy> > > >::correct() at ??:? #4  ? at ??:? #5  __libc_start_main in "/lib/x86_64-linux-gnu/libc.so.6" #6  ? at ??:? Aborted (core dumped)```

The log file of the solver is also attached:

Code:

```Solving for fluid region fluid DILUPBiCG:  Solving for Ux, Initial residual = 0.9997355, Final residual = 0.08277523, No Iterations 2 DILUPBiCG:  Solving for Uy, Initial residual = 0.9999186, Final residual = 0.07461577, No Iterations 2 DILUPBiCG:  Solving for Uz, Initial residual = 0.999995, Final residual = 0.05243879, No Iterations 2 DILUPBiCG:  Solving for h, Initial residual = 1, Final residual = 0.04643201, No Iterations 2 Min/max T:-2938920 1665459 GAMG:  Solving for p_rgh, Initial residual = 0.1680867, Final residual = 0.0009985177, No Iterations 6 time step continuity errors : sum local = 19589.79, global = 1565.821, cumulative = 1565.819 Min/max rho:2 2 DILUPBiCG:  Solving for epsilon, Initial residual = 0.9999723, Final residual = 2.378201e-09, No Iterations 1 DILUPBiCG:  Solving for k, Initial residual = 0.9999912, Final residual = 0.06906627, No Iterations 2 Solving for solid region box DICPCG:  Solving for h, Initial residual = 1, Final residual = 0.03971379, No Iterations 2 Min/max T:-264388.9 90652.27 Solving for solid region plate1 DICPCG:  Solving for h, Initial residual = 1, Final residual = 0.02562304, No Iterations 2 Min/max T:299.9961 300.0009 Solving for solid region plate2 DICPCG:  Solving for h, Initial residual = 1, Final residual = 0.03224597, No Iterations 2 Min/max T:299.9911 300.0009 Solving for solid region plate3 DICPCG:  Solving for h, Initial residual = 1, Final residual = 0.02419843, No Iterations 2 Min/max T:299.9997 300.0009 Solving for solid region hot1 DICPCG:  Solving for h, Initial residual = 0.8450844, Final residual = 0.005572694, No Iterations 2 Min/max T:300.0004 300.0031 Solving for solid region hot2 DICPCG:  Solving for h, Initial residual = 0.8459705, Final residual = 0.005387614, No Iterations 2 Min/max T:300.0005 300.003 Solving for solid region hot3 DICPCG:  Solving for h, Initial residual = 0.8490299, Final residual = 0.00578213, No Iterations 2 Min/max T:300.0004 300.003 ExecutionTime = 0.32 s  ClockTime = 0 s Time = 0.3 Solving for fluid region fluid DILUPBiCG:  Solving for Ux, Initial residual = 0.9586069, Final residual = 0.04442897, No Iterations 2 DILUPBiCG:  Solving for Uy, Initial residual = 0.9413187, Final residual = 0.02525996, No Iterations 2 DILUPBiCG:  Solving for Uz, Initial residual = 0.8798151, Final residual = 0.03200322, No Iterations 2 DILUPBiCG:  Solving for h, Initial residual = 0.9769101, Final residual = 0.01300722, No Iterations 2```

From, the log file, it can be seen that the value of time step continuity error is very large, may be this error is because of that.

Any help would be highly appreciated.

Thank you

 ingraban June 20, 2019 05:07

Here is an explanation of the term p_rgh:
Hydrostatic pressure effects

In your logfile for "solid region box", you get extraordinary temperatures min/max T:-264388.9 90652.27 K while everything else is at 300K. Could be that the trouble is caused there?

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