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July 6, 2015, 11:07 
Development of incompressible, temperature dependent solver

#1 
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Agustín Villa
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Hello,
I want to develope an incompressible solver where the density, heat capacity, thermal conductivity, viscosity... depend on the temperature, so I expect to see the buoyancy effects (Boussinesq is no applicable to my problem, neither the references I have found are clear in relation of its range of applications). So I want to integrate this in my solver. The properties are already defined as polynomial regressions, I have included the density and the heat capacity inside the derivatives... but since this is an incompressible solver, the pressure equations has to be defined also. I have to include rho as well as in the other equations, but it only gives me huge courant numbers, and finally my simulation crashes (if I run it with Boussinesq, or compressible solvers it does not crash, so it is not the set up but the pressure equation). Any of you have some experience on this? Thanks in advance! 

July 6, 2015, 15:26 

#2 
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Hello,
did you take into account, that in incompressible flow the equations in OpenFoam are divided through rho? Greetings 

July 7, 2015, 02:48 

#3 
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Agustín Villa
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Yes. In UEqn and TEqn everything is ok, the problem comes in the pEqn. I am not able to understand all the code, so I don't know where should I include the density.


July 7, 2015, 05:40 

#4 
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Agustín Villa
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Hello,
I think the problem is more related with this: Code:
Courant Number mean: 0 max: 0 Time = 0 DILUPBiCG: Solving for Ux, Initial residual = 1.428062e16, Final residual = 1.428062e16, No Iterations 0 DILUPBiCG: Solving for Uy, Initial residual = 2.792809e18, Final residual = 2.792809e18, No Iterations 0 DILUPBiCG: Solving for T, Initial residual = 1, Final residual = 4.894705e12, No Iterations 1 DICPCG: Solving for p_rgh, Initial residual = 1.085581e16, Final residual = 1.085581e16, No Iterations 0 DICPCG: Solving for p_rgh, Initial residual = 1.086498e16, Final residual = 1.086498e16, No Iterations 0 ExecutionTime = 1.16 s ClockTime = 2 s Courant Number mean: 9.354086e36 max: 2.343958e32 Time = 0 DILUPBiCG: Solving for Ux, Initial residual = 5.468248e20, Final residual = 5.468248e20, No Iterations 0 DILUPBiCG: Solving for Uy, Initial residual = 7.420473e20, Final residual = 7.420473e20, No Iterations 0 DILUPBiCG: Solving for T, Initial residual = 0.4145431, Final residual = 2.029354e12, No Iterations 1 DICPCG: Solving for p_rgh, Initial residual = 1, Final residual = 0.009628832, No Iterations 248 DICPCG: Solving for p_rgh, Initial residual = 2.703377e05, Final residual = 8.585544e07, No Iterations 223 ExecutionTime = 2.59 s ClockTime = 3 s Courant Number mean: 142726 max: 216211.7 Time = 0 DILUPBiCG: Solving for Ux, Initial residual = 0.9752576, Final residual = 5.325225e07, No Iterations 133 DILUPBiCG: Solving for Uy, Initial residual = 0.755965, Final residual = 8.880502e07, No Iterations 132 DILUPBiCG: Solving for T, Initial residual = 0.9999981, Final residual = 5.466545e08, No Iterations 88 DICPCG: Solving for p_rgh, Initial residual = 0.9907768, Final residual = 0.009654161, No Iterations 286 DICPCG: Solving for p_rgh, Initial residual = 0.001860895, Final residual = 9.4345e07, No Iterations 334 ExecutionTime = 6.48 s ClockTime = 7 s Courant Number mean: 94347.71 max: 239519 Time = 0 DILUPBiCG: Solving for Ux, Initial residual = 0.9781596, Final residual = 1.990685e07, No Iterations 11 DILUPBiCG: Solving for Uy, Initial residual = 0.9980529, Final residual = 5.394266e07, No Iterations 9 DILUPBiCG: Solving for T, Initial residual = 0.1367406, Final residual = 4.657122e07, No Iterations 11 DICPCG: Solving for p_rgh, Initial residual = 0.3061352, Final residual = 0.003004767, No Iterations 309 DICPCG: Solving for p_rgh, Initial residual = 0.002705098, Final residual = 9.266301e07, No Iterations 347 ExecutionTime = 8.49 s ClockTime = 9 s Courant Number mean: 5.062457e+07 max: 1.529998e+08 Time = 0 DILUPBiCG: Solving for Ux, Initial residual = 0.3327966, Final residual = 3.049949e07, No Iterations 17 DILUPBiCG: Solving for Uy, Initial residual = 0.2931983, Final residual = 9.687052e07, No Iterations 13 DILUPBiCG: Solving for T, Initial residual = 0.5618018, Final residual = 8.354536e07, No Iterations 13 DICPCG: Solving for p_rgh, Initial residual = 1, Final residual = 0.009164537, No Iterations 349 DICPCG: Solving for p_rgh, Initial residual = 0.01243677, Final residual = 9.123202e07, No Iterations 410 ExecutionTime = 10.82 s ClockTime = 11 s 

July 7, 2015, 06:46 

#5 
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ali alkebsi
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give more details
what solver do you use did you take an existing solver and modify on it are you sure you are not using a steady state solver (simpleFoam) 

July 7, 2015, 07:23 

#6  
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Agustín Villa
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Quote:
I have modified the buoyantBoussinesqPimpleFoam solver, where I include the density rho instead of rhok. Here you can see my equations: Code:
// Solve the Momentum equation mu=rho*turbulence>nu(); volScalarField muEff("muEff",mu+rho*turbulence>nut()); rhoPhi=linearInterpolate(rho*U) & mesh.Sf(); fvVectorMatrix UEqn ( fvm::ddt(rho, U) + fvm::div(rhoPhi, U)  fvm::laplacian(muEff,U)  fvc::div(muEff*dev2(fvc::grad(U)().T())) == fvOptions(rho, U) ); UEqn.relax(); fvOptions.constrain(UEqn); if (pimple.momentumPredictor()) { solve ( UEqn == fvc::reconstruct ( (  ghf*fvc::snGrad(rho)  fvc::snGrad(p_rgh) )*mesh.magSf() ) ); fvOptions.correct(U); } } Code:
volScalarField alphaEff("alphaEff", alpha + turbulenceThermal>alphat()); //alphaEff=alpha + turbulenceThermal>alphat(); volScalarField kThermalEff("kThermalEff",alphaEff*Cp*rho); rhoCpPhi = linearInterpolate(rho*Cp*U) & mesh.Sf(); fvScalarMatrix TEqn ( fvm::ddt(rho*Cp,T) + fvm::div(rhoCpPhi, T)  fvm::laplacian(kThermalEff, T) == fvOptions(rho*Cp,T) ); TEqn.relax(); fvOptions.constrain(TEqn); TEqn.solve(); //radiation>correct(); fvOptions.correct(T); Code:
volScalarField rAU(1.0/UEqn.A()); surfaceScalarField rAUf("rAUf", fvc::interpolate(rho*rAU)); volVectorField HbyA("HbyA", U); HbyA = rAU*UEqn.H(); surfaceScalarField phig(rAUf*ghf*fvc::snGrad(rho)*mesh.magSf()); surfaceScalarField phiHbyA ( "phiHbyA", ( (fvc::interpolate(rho*HbyA) & mesh.Sf()) + rAUf*fvc::ddtCorr(rho, U, rhoPhi) ) + phig ); fvOptions.makeRelative(fvc::interpolate(rho), phiHbyA); // Update the fixedFluxPressure BCs to ensure flux consistency setSnGrad<fixedFluxPressureFvPatchScalarField> ( p_rgh.boundaryField(), ( phiHbyA.boundaryField()  fvOptions.relative(mesh.Sf().boundaryField() & U.boundaryField()) *rho.boundaryField() )/(mesh.magSf().boundaryField()*rAUf.boundaryField()) ); while (pimple.correctNonOrthogonal()) { fvScalarMatrix p_rghEqn ( fvc::div(phiHbyA)  fvm::laplacian(rAUf, p_rgh) ); fvOptions.constrain(p_rghEqn); p_rghEqn.solve(mesh.solver(p_rgh.select(pimple.finalInnerIter()))); if (pimple.finalNonOrthogonalIter()) { // Calculate the conservative fluxes phi = (phiHbyA  p_rghEqn.flux())/fvc::interpolate(rho); // Explicitly relax pressure for momentum corrector p_rgh.relax(); // Correct the momentum source with the pressure gradient flux // calculated from the relaxed pressure U = HbyA + rAU*fvc::reconstruct((phig  p_rghEqn.flux())/rAUf); U.correctBoundaryConditions(); fvOptions.correct(U); } } p = p_rgh + rho*gh; 

July 7, 2015, 07:54 

#7 
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ali alkebsi
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Location: Strasbourg, France
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in UEqn
why dont you use + turbulence>divDevRhoReff(U) instead of  fvm::laplacian(muEff,U)  fvc::div(muEff*dev2(fvc::grad(U)().T())) ? in pEqn you should have the following surfaceScalarField rAUf("rAUf", fvc::interpolate(rAU)); and surfaceScalarField phiHbyA ( "phiHbyA", (fvc::interpolate(HbyA) & mesh.Sf()) + fvc::interpolate(rho*rAU)*fvc::ddtCorr(U, phi) ); phiHbyA += phig; or surfaceScalarField phiHbyA ( "phiHbyA", ( (fvc::interpolate(HbyA) & mesh.Sf()) + rAUf*fvc::ddtCorr(rho, U, rhoPhi) ) + phig ); you should have fvOptions.makeRelative(phiHbyA); not with rho you should have setSnGrad<fixedFluxPressureFvPatchScalarField> ( p_rgh.boundaryField(), ( phiHbyA.boundaryField()  fvOptions.relative(mesh.Sf().boundaryField() & U.boundaryField()) )/(mesh.magSf().boundaryField()*rAUf.boundaryField() ) ); you should have if (pimple.finalNonOrthogonalIter()) { phi = phiHbyA  p_rghEqn.flux(); p_rgh.relax(); U = HbyA + rAU*fvc::reconstruct((phig  p_rghEqn.flux())/rAUf); U.correctBoundaryConditions(); fvOptions.correct(U); } 

July 7, 2015, 07:56 

#8 
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ali alkebsi
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thats just another way of putting the equations and it follows the method used in vof solver
however why the time does not move is a mistry to me 

July 7, 2015, 08:16 

#9  
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Agustín Villa
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Quote:
Quote:
I have tried this, but the problem is still there. I think is related with the no advancing time, since Courant is increasing without control. 

July 8, 2015, 04:57 

#10 
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ali alkebsi
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can i ask how and where you defined your variable rho ?
and dont you expect a new source term to appear in the pressure equation due to the varying rho? 

July 8, 2015, 05:52 

#11  
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Agustín Villa
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Quote:
rho is defined in the createFields.H file: Code:
volScalarField rho ( IOobject ( "rho", runTime.timeName(), mesh, IOobject::NO_READ, IOobject::AUTO_WRITE ), // mesh baseRho+slopeRho*T+slope2Rho*T*T+slope3Rho*T*T*T+slope4Rho*T*T*T*T+slope5Rho*T*T*T*T*T ); Code:
surfaceScalarField phig(rAUf*ghf*fvc::snGrad(rho)*mesh.magSf()); 

July 8, 2015, 07:19 
laplacianFoam with sorce term

#12 
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vipin
Join Date: Jun 2015
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hi
I have created the laplacian foam with source term in user directory. how can i use this solver for my mesh? i got problem in compiling this solver plz help.. thanks in advanced vipin 

July 10, 2015, 06:43 

#13 
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ali alkebsi
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July 10, 2015, 09:40 

#14  
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Agustín Villa
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Quote:
Hello thanks for this idea. I will try it now! I will make you know if it is working. 

July 13, 2015, 10:40 

#15 
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Agustín Villa
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Hello,
I have included the rhoEqn in my case, and now the time is increasing! But I still have convergence problems, and my Courant number seems to be always equal to zero: Code:
Starting time loop Reading surface description: zPlane Time = 0 Courant Number mean: 0 max: 0 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 DILUPBiCG: Solving for Ux, Initial residual = 0.9973808, Final residual = 7.190542e23, No Iterations 3 DILUPBiCG: Solving for Uy, Initial residual = 0.9977049, Final residual = 7.22382e23, No Iterations 3 DILUPBiCG: Solving for T, Initial residual = 1, Final residual = 2.407855e27, No Iterations 2 DICPCG: Solving for p_rgh, Initial residual = 0.008707272, Final residual = 8.686427e08, No Iterations 305 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 0, global = 0, cumulative = 0 DICPCG: Solving for p_rgh, Initial residual = 0.9915434, Final residual = 9.755695e16, No Iterations 540 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 0, global = 0, cumulative = 0 ExecutionTime = 3.53 s ClockTime = 4 s Time = 0.0001 Courant Number mean: 0 max: 0 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 DILUPBiCG: Solving for Ux, Initial residual = 0.2423949, Final residual = 4.052451e16, No Iterations 2 DILUPBiCG: Solving for Uy, Initial residual = 0.7640606, Final residual = 2.225911e16, No Iterations 2 DILUPBiCG: Solving for T, Initial residual = 0.4897039, Final residual = 1.178537e27, No Iterations 2 DICPCG: Solving for p_rgh, Initial residual = 1, Final residual = 9.357006e06, No Iterations 365 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 0, global = 0, cumulative = 0 DICPCG: Solving for p_rgh, Initial residual = 0.6779252, Final residual = 8.230382e15, No Iterations 1001 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 0, global = 0, cumulative = 0 ExecutionTime = 7.06 s ClockTime = 7 s Time = 0.0002 Courant Number mean: 0 max: 0 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 DILUPBiCG: Solving for Ux, Initial residual = 0.4997963, Final residual = 2.599016e16, No Iterations 72 DILUPBiCG: Solving for Uy, Initial residual = 0.8234894, Final residual = 4.587841e16, No Iterations 81 DILUPBiCG: Solving for T, Initial residual = 0.9999986, Final residual = 5.121843e16, No Iterations 16 DICPCG: Solving for p_rgh, Initial residual = 0.9987744, Final residual = 9.690122e06, No Iterations 418 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 0, global = 0, cumulative = 0 DICPCG: Solving for p_rgh, Initial residual = 0.4040092, Final residual = 0.2838411, No Iterations 1001 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 0, global = 0, cumulative = 0 ExecutionTime = 11.66 s ClockTime = 12 s Time = 0.0003 Courant Number mean: 0 max: 0 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 DILUPBiCG: Solving for Ux, Initial residual = 0.7760858, Final residual = 2.422542e16, No Iterations 33 DILUPBiCG: Solving for Uy, Initial residual = 0.729375, Final residual = 7.134555e16, No Iterations 33 DILUPBiCG: Solving for T, Initial residual = 0.4481602, Final residual = 2.430657e16, No Iterations 36 DICPCG: Solving for p_rgh, Initial residual = 0.9999992, Final residual = 9.311596e06, No Iterations 738 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 0, global = 0, cumulative = 0 DICPCG: Solving for p_rgh, Initial residual = 0.5479091, Final residual = 31.94313, No Iterations 1001 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 0, global = 0, cumulative = 0 ExecutionTime = 16.75 s ClockTime = 17 s Time = 0.0004 Courant Number mean: 0 max: 0 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 DILUPBiCG: Solving for Ux, Initial residual = 0.9067029, Final residual = 4.97392e16, No Iterations 9 DILUPBiCG: Solving for Uy, Initial residual = 0.7489127, Final residual = 3.218888e18, No Iterations 10 DILUPBiCG: Solving for T, Initial residual = 0.5418659, Final residual = 1.234434e16, No Iterations 15 DICPCG: Solving for p_rgh, Initial residual = 1, Final residual = 1810.988, No Iterations 1001 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 0, global = 0, cumulative = 0 DICPCG: Solving for p_rgh, Initial residual = 0.7886131, Final residual = 286.9007, No Iterations 1001 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 0, global = 0, cumulative = 0 ExecutionTime = 22.1 s ClockTime = 22 s Time = 0.0005 Courant Number mean: 0 max: 0 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 DILUPBiCG: Solving for Ux, Initial residual = 0.9805554, Final residual = 8.929525e17, No Iterations 9 DILUPBiCG: Solving for Uy, Initial residual = 0.9615684, Final residual = 3.209775e16, No Iterations 8 DILUPBiCG: Solving for T, Initial residual = 0.9894829, Final residual = 7.77986e16, No Iterations 10 DICPCG: Solving for p_rgh, Initial residual = 1, Final residual = 1199.078, No Iterations 1001 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 0, global = 0, cumulative = 0 DICPCG: Solving for p_rgh, Initial residual = 7.390336e05, Final residual = 1.163134, No Iterations 1001 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 0, global = 0, cumulative = 0 ExecutionTime = 27.23 s ClockTime = 27 s Time = 0.0006 Courant Number mean: 0 max: 0 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 DILUPBiCG: Solving for Ux, Initial residual = 0.6522411, Final residual = 1.133062e18, No Iterations 8 DILUPBiCG: Solving for Uy, Initial residual = 0.8703662, Final residual = 7.707482e17, No Iterations 7 DILUPBiCG: Solving for T, Initial residual = 0.1164554, Final residual = 1.04748e16, No Iterations 10 DICPCG: Solving for p_rgh, Initial residual = 1, Final residual = 8.014764, No Iterations 1001 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 0, global = 0, cumulative = 0 DICPCG: Solving for p_rgh, Initial residual = 1.679593e05, Final residual = 494607.5, No Iterations 1001 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 time step continuity errors : sum local = 0, global = 0, cumulative = 0 ExecutionTime = 32.36 s ClockTime = 33 s Time = 0.0007 Courant Number mean: 0 max: 0 diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 #0 Foam::error::printStack(Foam::Ostream&) at ??:? #1 Foam::sigFpe::sigHandler(int) at ??:? #2 at sigaction.c:? #3 double Foam::sumProd<double>(Foam::UList<double> const&, Foam::UList<double> const&) at ??:? #4 Foam::PBiCG::solve(Foam::Field<double>&, Foam::Field<double> const&, unsigned char) const at ??:? #5 at ??:? #6 at ??:? #7 at ??:? #8 at ??:? #9 __libc_start_main at ??:? #10 at ??:? Floating point exception Code:
{ volScalarField rAU(1.0/UEqn.A()); surfaceScalarField rAUf("rAUf", fvc::interpolate(rho*rAU)); volVectorField HbyA("HbyA", U); HbyA = rAU*UEqn.H(); surfaceScalarField phig(rAUf*ghf*fvc::snGrad(rho)*mesh.magSf()); surfaceScalarField phiHbyA ( "phiHbyA", ( (fvc::interpolate(rho*HbyA) & mesh.Sf()) + rAUf*fvc::ddtCorr(rho, U, rhoPhi) ) + phig ); fvOptions.makeRelative(phiHbyA); // Update the fixedFluxPressure BCs to ensure flux consistency setSnGrad<fixedFluxPressureFvPatchScalarField> ( p_rgh.boundaryField(), ( phiHbyA.boundaryField()  fvOptions.relative(mesh.Sf().boundaryField() & U.boundaryField()) *rho.boundaryField() )/(mesh.magSf().boundaryField()*rAUf.boundaryField()) ); // Info<<"phiHbyA" << phiHbyA<< endl; // // Info<<"rAUf" << rAUf<< endl; // Info<<"p_rgh" << p_rgh<< endl; fvScalarMatrix p_rghDDtEqn ( //fvc::ddt(rho) //+ psi*correction(fvm::ddt(p_rgh)) fvc::div(phiHbyA)  fvm::laplacian(rAUf, p_rgh) // == // fvOptions(p_rgh) ); while (pimple.correctNonOrthogonal()) { fvScalarMatrix p_rghEqn ( p_rghDDtEqn ); fvOptions.constrain(p_rghEqn); p_rghEqn.solve(mesh.solver(p_rgh.select(pimple.finalInnerIter()))); if (pimple.finalNonOrthogonalIter()) { // Calculate the conservative fluxes rhoPhi = phiHbyA  p_rghEqn.flux(); // Explicitly relax pressure for momentum corrector p_rgh.relax(); // Correct the momentum source with the pressure gradient flux // calculated from the relaxed pressure U = HbyA + rAU*fvc::reconstruct((phig  p_rghEqn.flux())/rAUf); U.correctBoundaryConditions(); fvOptions.correct(U); } } p = p_rgh + rho*gh; #include "densityEqn.H" #include "continuityErrs.H" } 

July 15, 2015, 08:11 

#16  
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Agustín Villa
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Quote:
It only remains to see if it is going ok now. In relation with the rhoEqn.H, I have disabled it. 

August 6, 2015, 09:08 

#17 
Senior Member
Agustín Villa
Join Date: Apr 2013
Location: Brussels
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Hello,
first of all, I was able to create the solver! Now, I am dealing with the set up of the case. Base in compressible equations (I am simulating air), I should expect some turbulence in my case. The problem comes when, by using the same BC for T and U, there is not! If I use Boussinesq, I am able to see the turbulence, but temperature differences are long (we speak about 100K). In the other case, by using temperature dependence, the differences are around 20K. Does anyone up to when Boussinesq is a good approximation? (not for my case, but just to know, since there are not general indications) 

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