[pvs9]

Hi there!
I am new using OpenFOAM and would like to share a few questions with you.
I am currently developing a steady state thermal model (chtMultiRegionSimpleFoam) that consists of a building with two inlets windows at the side and one outlet window at the top. Inside it, I have placed a heat source. I wanna evaluate natural convection occurring inside the building, as well as the temperatures and velocities around the model.
I am not sure about which BC I should use for the inlet and outlet windows.
Has anyone done something similar?

Thank you!

Paola.

[pupo]

First of all, may I ask why use the CHTMultiRegion? it seems liek your problem considers only flow.

Anyway. I'm dealing with a similar problem (flow inside an annulus) and so far the only boundary conditions that work are:

U:
   Outlet        { type zeroGradient; } 
   Inlet         { type zeroGradient; } 

P_rgh:
    Inlet          { type fixedValue; value uniform 101325; }
    Outlet         { type zeroGradient; }

T:

   Inlet         { type fixedValue; value uniform 293.7;}
   Outlet        { type zeroGradient; }

The catch is, this only works if the outlet is at z = 0. This makes no sense and I'm yet to figure out why this is necessary.


Also, check this thread ( http://www.cfd-online.com/Forums/ope...-behavior.html ) to see how i changed the initial solution of the problem. It also works in buoyantSimpleFoam and CHTMultiRegionSimpleFoam with some minor changes. IT greatly increases convergence speed.

[pvs9]

Hi Pedro! thank you so much for your reply.


Actually my problem has a few solid regions (building, heater, floor) and one fluid region (air), that's why I'm using chtMultiRegionSimpleFoam. I ran my case with the boundary conditions you said but it didn't work (maximum number of iterations exceeded). I've tried a bunch of different BC and sometimes I manage to obtain good temperature values, but the wallHeatFluxes at the BC doesn't have much sense (the flux between interfaces is correct, but at the boundaries it's not working well since the energy balance has no sense at all, do you know why is that?)

Paola

[pvs9]

Hello!

I'd like to run a transient case where the temperature of the BC varies with time. The geometry of my case is the same as before, so I'm using chtMultiRegionFoam since I have solid and fluid regions, but after 10 iterations, I get this error:

 
Time = 1

Solving for fluid region Aire
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
DILUPBiCG:  Solving for Ux, Initial residual = 0.5670344, Final residual = 2.619258e-08, No Iterations 47
DILUPBiCG:  Solving for Uy, Initial residual = 0.4106254, Final residual = 7.722867e-08, No Iterations 48
DILUPBiCG:  Solving for Uz, Initial residual = 0.5202844, Final residual = 3.483137e-08, No Iterations 48
DILUPBiCG:  Solving for h, Initial residual = 0.1934812, Final residual = 2.74785e-08, No Iterations 46
Min/max T:284.3531 390.5775
GAMG:  Solving for p_rgh, Initial residual = 0.8751491, Final residual = 0.00850716, No Iterations 8
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors (Aire): sum local = 0.04660027, global = 0.0085699, cumulative = 0.007883122
#0  Foam::error::printStack(Foam::Ostream&) in "/opt/openfoam222/platforms/linuxGccDPOpt/lib/libOpenFOAM.so"
#1  Foam::sigFpe::sigHandler(int) in "/opt/openfoam222/platforms/linuxGccDPOpt/lib/libOpenFOAM.so"
#2  Uninterpreted: 
#3  Foam::GAMGSolver::scale(Foam::Field<double>&, Foam::Field<double>&, Foam::lduMatrix const&, Foam::FieldField<Foam::Field, double> const&, Foam::UPtrList<Foam::lduInterfaceField const> const&, Foam::Field<double> const&, unsigned char) const in "/opt/openfoam222/platforms/linuxGccDPOpt/lib/libOpenFOAM.so"
#4  Foam::GAMGSolver::Vcycle(Foam::PtrList<Foam::lduMatrix::smoother> const&, Foam::Field<double>&, Foam::Field<double> const&, Foam::Field<double>&, Foam::Field<double>&, Foam::Field<double>&, Foam::PtrList<Foam::Field<double> >&, Foam::PtrList<Foam::Field<double> >&, unsigned char) const in "/opt/openfoam222/platforms/linuxGccDPOpt/lib/libOpenFOAM.so"
#5  Foam::GAMGSolver::solve(Foam::Field<double>&, Foam::Field<double> const&, unsigned char) const in "/opt/openfoam222/platforms/linuxGccDPOpt/lib/libOpenFOAM.so"
#6  Foam::fvMatrix<double>::solveSegregated(Foam::dictionary const&) in "/opt/openfoam222/platforms/linuxGccDPOpt/lib/libfiniteVolume.so"
#7  Foam::fvMatrix<double>::solve(Foam::dictionary const&) in "/opt/openfoam222/platforms/linuxGccDPOpt/bin/chtMultiRegionFoam"
#8  
 in "/opt/openfoam222/platforms/linuxGccDPOpt/bin/chtMultiRegionFoam"
#9  __libc_start_main in "/lib/i386-linux-gnu/libc.so.6"
#10  
 in "/opt/openfoam222/platforms/linuxGccDPOpt/bin/chtMultiRegionFoam"
Excepción de coma flotante (`core' generado)

Thank you for any help, I really appreciate it .


Paola

[pvs9]

Hi everybody!

After 26 different cases, here is my conclusion: you can obtain a very stable configuration by setting the inlet velocity and the pressure at the outlet, so I'm gonna write the boundary conditions for the fluid region that I used.

Velocity:
inlet- fixedValue
outlet- inletOutlet

Temperature:
inlet- fixedValue
outlet- inletOutlet

Pressure:
inlet - zeroGradient
outlet - fixedValue

Hope it's useful for you!