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-   -   Buoyant Axisymmetric Plumes (http://www.cfd-online.com/Forums/openfoam-solving/60270-buoyant-axisymmetric-plumes.html)

imago March 27, 2006 11:25

Hi, i am trying to run a ca
 
Hi,

i am trying to run a calculation with buoyantFoam related to a simple plume simulation for an axisymmetric problem. The boundary conditions that i have selected are empty(Symmetry-Axis), Inlet (fixed Values for Temperature and velocity) and pressure outlet (for the side and the top of the computational domain). The initial velocity Fields for the internal Mesh are set to be zero.
The calculation does not converge (nan for the Courandt Numbers and the convergence parameters).
Now i would to ask you:

1.) handles the buoyantFoam solver compressible Flows (variabel density case and low mach number) or the bousinesq approximation?

2.) Because i have trying various combinations of discretization schemes, could anybody gives to me informations abbout suggested initial Field values?

eugene March 27, 2006 12:03

One thing I can tell you about
 
One thing I can tell you about buoyant calculations from painfull personal experience: make 100% sure all your wall and inlet pressure boundaries are defined as "wallBuoyantPressure" and not "zeroGradient" otherwise you will never converge.

imago March 27, 2006 12:41

i have now select the fixedTem
 
i have now select the fixedTemperatureWall option with fixed velocity (as this is the case in the inlet boundary) for the previously as inlet defined region. This allows for to define a "wallBuoyantPressure" but the code writes an errormessage out with the suggestion to use "zeroGradient" for kinetic Energy k in the same boundary.
What can i do?

eugene March 27, 2006 12:44

Submit a bug report and then f
 
Submit a bug report and then fire up your favourite text editor and change the entries manually.

imago March 27, 2006 12:48

Thanks Eugene i will follow
 
Thanks Eugene

i will follow your suggestions.

imago March 27, 2006 13:07

i have edit manually the k-sou
 
i have edit manually the k-source-file in the 0-directory but now the calculation does not converge.
Nothing is so simple as like it looks before.

eugene March 27, 2006 13:35

why did you edit the k file? B
 
why did you edit the k file? Buoyancy has no effect on k and epsilon BCs. You should use fixedValue for k at the inlet.
You need wallBuoyantPressure for p at all boundaries where it is usually zeroGradient.

imago March 28, 2006 06:11

now i have edit the pressure b
 
now i have edit the pressure boundaries in the p-file (Directory 0), so the zeroGradient condition becomes to wallBuoyantPressure and the fixed Value conditions (outlets at top and side) remains as is.
But even the Courandt Numbers are inacceptable and the flow behaves like inviscid Fluid where the inlet velocity remains constant throughout the computational domain and no turbulence effects affects the flow in the sense of developed eddy dissipation and velocity componets coupling.
The FluidMixture is air as prescribed in the code, so i dont thing that the thermophysical properties are poorely chosen.

eugene March 28, 2006 08:16

So what is your inlet value fo
 
So what is your inlet value for k and epsilon?
Is the turbulence solver doing anything?

imago March 28, 2006 09:19

i make various gues for k like
 
i make various gues for k like:

k=3/2 (u_fluct)**2

last value k=0.024

but these makes the convergence to be more defecault.
The convergence monitor shows only details for the velocity components and the variable pb.

eugene March 28, 2006 13:21

Well if it isnt showing conver
 
Well if it isnt showing convergence info for k and epsilon, you are not solving for turbulence. Check your constant/turbulenceProperties dictionary. turbulence should be "on" and the turbulence model should be set to something other than laminar.

imago March 29, 2006 06:52

The turbulence modell is set t
 
The turbulence modell is set to kEpsilon and the turbulence is on.
In the solution outputs (t-Directories) are files with information about these properties but the values shows not changes.
In FoamX are the related inputs also selected!


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