# Buoyantboussinesq simpleFoam residuals problem

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March 16, 2015, 06:11
Buoyantboussinesq simpleFoam residuals problem
#1
Member

Naresh Yathuru
Join Date: Feb 2015
Posts: 66
Rep Power: 9
Hi foamers,

I m simulating a room with a inlet and outlet and a rectangular patch called lighting on the ceiling and cube inside the room.
As a first basic simulation I wanted to specify heat flux boundary condition for the patch and temperature to the inlet air and velocity at the inlet pressure at outlet by pressure i mean (p_rhg) as p is calculated at the outlet.

problem:
1. i did a couple of simulation but in both the simulations i get a huge fluctuatioin in the residuals graph. i have attached the picture below.
I m attaching my fvscheme and fvsoluion here :

FV scheme

ddtSchemes
{
}

{
default leastSquares; // it was Gauss linear
}

divSchemes
{
default none;
div(phi,U) bounded Gauss linearUpwind grad(U); // was bounded Gauss upwind which is first order but linearupwind is second order
//div(phi,U) bounded Gauss upwind;
div(phi,k) bounded Gauss upwind;
//div(phi,T) bounded Gauss upwind;
div(phi,epsilon) bounded Gauss upwind;
div(phi,omega) bounded Gauss upwind;
div(phi,R) bounded Gauss upwind;
div(R) Gauss linear;
div(phi,nuTilda) bounded Gauss upwind;
}

laplacianSchemes
{
default Gauss linear corrected;
}

interpolationSchemes
{
default linear;
}

{
default corrected;
}

fluxRequired
{
default no;
p_rgh ;
}

// ************************************************** *********************** //
FV solution:
solvers
{
p_rgh
{
solver PCG;
preconditioner DIC;
tolerance 1e-8;
relTol 0.001;
}

"(U|T|k|epsilon|omega|R)"
{
solver PBiCG;
preconditioner DILU;
tolerance 1e-8; // before 1e-05
relTol 0.001;
}
}

SIMPLE
{
nNonOrthogonalCorrectors 0;
pRefCell 0;
pRefValue 0;

/*residualControl
{
p_rgh 1e-2;
U 1e-4;
T 1e-2;

// possibly check turbulence fields
"(k|epsilon|omega)" 1e-3;
}*/
}

relaxationFactors
{
fields
{
p_rgh 0.3; //before it was 0.7
}
equations
{
U 0.7; // before it was 0.3
T 0.5;
"(k|epsilon|omega|R)" 0.7;
}
}

sorry for the long question.

Additionally i didnot get the correct results for the simulation.

thankyou

With Regards,
Naresh Yathuru
Attached Images
 Bildschirmfoto-5.jpg (28.9 KB, 32 views)

 March 16, 2015, 09:33 #2 Member   Thiago Parente Lima Join Date: Sep 2011 Location: Diamantina, Brazil. Posts: 54 Rep Power: 12 Hi Naresh Yathuru, It seems that you didn't achieve convergence for your problem. So instead of posting fvSolutions and fvSchemes, it would be better to post your boundary conditions. I suggest you to use the 1st order upwind scheme for the divergence therms unless you achieve convergence. You may use [ code] text [ /code] (without spaces) when posting pieces of code. Regards, __________________ Fields of interest: Heat transfer; Convection heat transfer; Conjugate heat transfer.

 March 17, 2015, 03:52 #3 Member   Naresh Yathuru Join Date: Feb 2015 Posts: 66 Rep Power: 9 Thank you so much thiago. I think my alphat,epsillon,k,nu,Omega B.C are fine. could you please have a look at my p, p-rgh, u, T Code: ```FoamFile { version 2.0; format ascii; class volScalarField; object p; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // dimensions [0 2 -2 0 0 0 0]; internalField uniform 0; boundaryField { inlet { type zeroGradient; } outlet { type fixedValue; value uniform 0; //before \$internalField; } sideandfloorwalls { type calculated; value \$internalField; } innercube { type calculated; value \$internalField; } lightingwall { type calculated; value \$internalField; } roof { type calculated;// before it was calculated; value \$internalField; } } //``` This is my p-rgh Code: ```FoamFile { version 2.0; format ascii; class volScalarField; object p_rgh; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // dimensions [0 2 -2 0 0 0 0]; internalField uniform 0; boundaryField { inlet { type zeroGradient; //rho rhok; //value uniform 0; } outlet { type fixedValue; value uniform 0; } sideandfloorwalls { type fixedFluxPressure; rho rhok; value uniform 0; } innercube { type fixedFluxPressure; rho rhok; value uniform 0; } lightingwall { type fixedFluxPressure; rho rhok; value uniform 0; } roof { type fixedFluxPressure; rho rhok; value uniform 0; } } // ************************************************************************* //``` Code: ```version 2.0; format ascii; class volScalarField; object T; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // dimensions [0 0 0 1 0 0 0]; internalField uniform 293; //17C boundaryField { inlet { type fixedValue; value uniform 293.15; // 20C } outlet { type zeroGradient; } sideandfloorwalls { type zeroGradient; } lightingwall { //type wallHeatFlux; //heatFlux uniform -200; // This did not work for incompressible flows. I read somewhere that this B:C does not exist in OF 230 type turbulentHeatFluxTemperature; heatSource flux; q uniform -200; // w/m^2 // This is just a check . this would generate a surface temperature of -27 C alphaEff alphaEff; value uniform 273; // place holder } /*{ type fixedValue; value uniform 323.15; // for the time being or flux 100 w/m }*/ innercube { type zeroGradient; //value uniform 313.15; } roof { type zeroGradient; //value uniform 291.15; } } // ************************************************************************* //``` U was initialised with potentialFoam: Code: ```dimensions [0 1 -1 0 0 0 0]; internalField uniform (0 0 0); boundaryField { inlet { type fixedValue; value uniform (1 0 0); } outlet { type zeroGradient; } sideandfloorwalls { type fixedValue; value uniform (0 0 0); } innercube { type fixedValue; value uniform (0 0 0); } lightingwall { type fixedValue; value uniform (0 0 0); } roof { type fixedValue; value uniform (0 0 0); } } // ************************************************************************* //``` FYI: yesterday i came to know that TurbulentHeatFluxTemperature boundary condition has a bug from the post of Bruno http://www.cfd-online.com/Forums/ope...le-case-2.html I may not be good in programming but i m good in sharing information Thats all i can contribute for OF users. regards, Naresh

 March 17, 2015, 03:56 #4 Member   Naresh Yathuru Join Date: Feb 2015 Posts: 66 Rep Power: 9 By the way i m using OF 230. i dont know if the TurbulentHeatFluxTemperature bug is fixed in OF 231. Naresh

 March 17, 2015, 07:07 #5 Member   Thiago Parente Lima Join Date: Sep 2011 Location: Diamantina, Brazil. Posts: 54 Rep Power: 12 Hi Naresh, Unfortunately I don't have much to contribute, but I woud suggest you to use the fixedFluxPressure as inlet BC for p_rgh (see here and here) and zeroGredient for oulet BC for p_rgh. I don't know much about the lightingwall BC, but I suggest you to first try a fixedValue BC and see if the problem converges and then change this BC (a step by step thing ) Regards, __________________ Fields of interest: Heat transfer; Convection heat transfer; Conjugate heat transfer.

March 17, 2015, 10:40
#6
Member

Naresh Yathuru
Join Date: Feb 2015
Posts: 66
Rep Power: 9
hi thiago,

Thank for your reply. I have a very crucial question i hope you could help me. I m sorry for asking it in the same thread. I m using buoyantBoussinesqsimple Foam. i m using the turbulentHeatFluxTemperature which is not giving me the reselt i expected (image attached)
1. does the turbulentHeatFluxTemperature really has a bug to be concerned about?
If yes then i really surprised that no one found it out untill now except bruno untill nov 2014.

2. if not could u please check if my boundary conditions are correct.

as u can see from my boundar condition for temperature. the temperature cannot be greater than 293 K.

I m totally confused. where is the problem . is it because of the heatflux b.C or any other boundary condition.

I ran the same simulation in fluent the results are fine.

then i tried to simulate with temperature boundary condition for the lightingwall then every thing was fine.

3. is there another possibility to specify the heat flux B.c?

naresh
Attached Images
 pic.jpg (33.2 KB, 16 views) fluent.jpg (18.9 KB, 9 views)

 March 20, 2015, 14:33 #7 Member   Thiago Parente Lima Join Date: Sep 2011 Location: Diamantina, Brazil. Posts: 54 Rep Power: 12 Hi Nares, Answering your questions: 1. I really don't know, but is always better do use the latest versions to avoid problems with bugs already solved. 2. The suggestions I have were that of my last post. I only solved closed problems in OF, so I've never dealt with inlet or oulet BC. 3. You can use the fixedGradient BC to specify a fixed heat flux. Regards, __________________ Fields of interest: Heat transfer; Convection heat transfer; Conjugate heat transfer.