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-   -   BC types in OpenFoam (http://www.cfd-online.com/Forums/openfoam-pre-processing/62076-bc-types-openfoam.html)

erik_bjorn October 24, 2007 02:40

I am new to OpenFoam. Can some
 
I am new to OpenFoam. Can someone tell where to find more information about the different boundary conditions, apart from table 6.4. in the user guide? I have already searched this forum, and I am aware that the information is available in the code. However, I cannot understand the code. Is there a plain-text description somewhere?

gschaider October 24, 2007 07:27

I'm afraid: No
 
I'm afraid: No

graser November 19, 2007 07:24

Hi Erik Look here for the b.c
 
Hi Erik
Look here for the b.c.:

.../OpenFOAM/src/finiteVolume/fields/fvPatchFields/derived

There you will find the different boundary conditions - some even with a short description and example - if you open the *.C and *.H files with an editor

erik_bjorn November 20, 2007 03:26

Thank you for the tip. However
 
Thank you for the tip. However, I cannot see much in the way of descriptions. At least not in a form understandable to me. But then again, I'm just a simple engineer, not an expert in CFD and C++ programming.

graser November 20, 2007 04:56

And I'm just a Student in the
 
And I'm just a Student in the 2nd year and neighter a C++ expert http://www.cfd-online.com/OpenFOAM_D...part/happy.gif
The description I'm talking of is not in the code; its in the "foreword" just below the GNU License written as a comment
Look at
fvPatchFields/derived/massFlowRateInletVelocity.H
(open with an editor) for example; there you can see a good description how to use this boundary in the comments

erik_bjorn November 20, 2007 06:03

OK, I see what you mean now. T
 
OK, I see what you mean now. Thanks. I am afraid the description is missing in many of the BC's. But at least now I know where to look for them in future versions.

graser November 20, 2007 06:48

Is the shown description what
 
Is the shown description what you're looking for?
Maybe I can help with a few of the others where the description is missing.
Also there are some descriptions of boundarys throughout this forum; you just have to search a little.

erik_bjorn November 20, 2007 07:41

Yes, the shown description is
 
Yes, the shown description is a great help. Right now, I am interested in finding out the differences between different boundaries to do with pressure:
totalPressure
pressureInletVelocity
pressureInletUniformVelocity
pressureInletOutletVelocity
pressureDirectedInletVelocity
pressureDirectedInletOutletVelocity
fixedFluxPressure
fixedFluxBuoyantPressure
freestreamPressure

graser November 20, 2007 08:05

Have you looked at the User Ma
 
Have you looked at the User Manual?
pressureInletVelocity
totalPressure
pressureInletOutletVelocity
pressureDirectedInletVelocity
pressureDirectedInletOutletVelocity
are explained in Cahpter 6.2/Table 6.4/ page U-141

fixedFluxPressure
I'd guess is a BC where you set the Flux as a fixedValue an the Pressure is calculated according to the Flux

fixedFluxBuoyantPressure
should be almost the same with additional heattransfer (->buoyant) but i realy dont know it exactly

additional info:
http://www.cfd-online.com/OpenFOAM_D...tml?1175063998

there are a lot more BC topics in the forum...search it http://www.cfd-online.com/OpenFOAM_D...part/happy.gif

erik_bjorn November 20, 2007 08:06

Maybe I should describe the pr
 
Maybe I should describe the problems I am presently working with. Maybe somebody can tell me what to do:

Problem 1:
Cross-contamination (or short-circuit) from a ventilation exhaust to an intake (on the outside of a building), under influence of wind. The exhaust and intake can both be either constant velocity or mass flow boundaries. Wind must be velocity boundary. I need a "far field" boundary, which I think should be "constant pressure". How do I implement this in OF?

Problem 2:
A fan blows air through a heat exchanger via an irregular duct geometry. The heat exchanger consists of very many fine plates, which I don't want to simulate. I know how the heat exchanger behaves with regard to pressure drop. I imagine I can simulate it as a pressure boundary, I am just unsure which is appropriate.

graser November 20, 2007 08:10

I'd say "far field" is the sam
 
I'd say "far field" is the same as "freestream"

onurdundar March 24, 2008 18:33

Hi I am new OpenFoam user is
 
Hi
I am new OpenFoam user is there any Boundary condition which represents uniform flow in Open channel. I tried fixed velocity but caused problem just connected to the atmosphere patch.
In fact I saw many different type of boundary condition in field library. For example I tried massFlowRateInletVelocity in 0/U file
type massFlowRateInletVelocity
value 12.849
but this gave error
How can I understand the correct information from .C file of .H file of that boundary condition.

waynezw0618 April 14, 2008 03:50

Hi try inlet { type mas
 
Hi
try

inlet
{
type massFlowRateInletVelocity
massFlowRate 0.2// 0.2kg s^-1

}

jason April 17, 2008 10:32

Hi, Section 6.2.3 of the us
 
Hi,

Section 6.2.3 of the user guide tells me that there is a boundary type called 'calculated' where the boundary field is derived from other fields. I have tried searching the forum but cannot really find anything about how to use this. I'm curious about two things.

1/ I want to set the flowrate at an inlet to a certain value that is found from a polynomial that relates the flowrate and pressure, eg a polynomial fitted to a centrifugal pump Flowrate-Pressure curve. So, based on the pressure at the last timestep, I adjust the flowrate at the boundary in order to mimic the response of a centrifugal pump.

2/ Is it possible to have a pair of boundaries in unconnected meshes where the fluid flowing into one boundary is set from the fluid flowing out of the other boundary. So, that if I managed to do No 1 I could adjust the flowrates in the unconnected meshes automatically.

Is this possible or do I have to do some programming.

Thanks

Jason

prapanj August 11, 2009 03:56

Hey,

there is something called the directMapped boundary, where you can set your inlet as the flow at another patch witch is x distance in front or behind it.

prapanj August 11, 2009 09:38

Hey,

there is something called the directMapped boundary, where you can set your inlet as the flow at another patch witch is x distance in front or behind it.

ksookhak October 24, 2009 12:21

Robin B.C
 
Hi

Does anyone know how shall I model the following Robin B.C?

dC/dY=alpha*C

where C is the scalar concentration, alpha is constant and Y is the wall-normal direction.
It means the gradient is proportional to the concentration which is not known a priori.

Thanks in advance
Kaveh

idrama December 16, 2009 05:01

Hey folks!

I created a geometry and a mesh in salome. My mesh contains patches in the interior of the geometry. Does anybody know how to set a "continuity patch" in OpenFOAM?


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