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Old   May 7, 2010, 07:16
Default List/documentation of all BC/patch types of the OF solvers
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Christoph
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Hello,

being new to OpenFOAM, I am wondering if there is a list of all possible BC/type of patches (e.g. zeroGradient, fixedValue, etc.) for each solver type, accompanied with a little documentation? Using e.g. k-eps models, I have wall-functions a.s.o.

Using the text-editor for setting up my BCs and patch-types, I am completely lacking a naming-list of the BCs, I am having a hard time guessing the correct nomenclature.

I would appreciate any help!
Best regards,
Kriz
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Old   May 7, 2010, 07:19
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Johan Spång
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http://www.openfoam.com/docs/user/

see chapter 5 for some information about boundary conditions and chapter 7 for information about turbulence.

Quote:
Originally Posted by kriz View Post
Hello,

being new to OpenFOAM, I am wondering if there is a list of all possible BC/type of patches (e.g. zeroGradient, fixedValue, etc.) for each solver type, accompanied with a little documentation? Using e.g. k-eps models, I have wall-functions a.s.o.

Using the text-editor for setting up my BCs and patch-types, I am completely lacking a naming-list of the BCs, I am having a hard time guessing the correct nomenclature.

I would appreciate any help!
Best regards,
Kriz
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Old   May 7, 2010, 07:37
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Quote:
Originally Posted by josp View Post
Thanks for the quick reply, but, of course, I have already consulted the manual. It leaves much more questions open than it answers.

There is one table on page 133 stating some BCs of different types, however, not explaining them.

For example, "turbulentInlet" "calculates a fluctuating variable based on a scale of a mean value" and I have to specify a reference Field and a fluctuation scale. So I am as lucky as before. What is the fluctuation scale? The characteristic turbulent scale? What reference field? To what variable I can specify this BC to? Velocity?

Simple example: I want to specify a fixed value velocity BC at an inlet and a fixed value pressure BC at the outlet, what do I have to specify for pressure at the inlet and for velocity at the outlet?
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Old   May 7, 2010, 08:09
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In OpenFOAM you have to specify BC's for each equation separately

For your simple example with fixedValue U and fixedValue p on inlet and outlet see:
/home/foam/OpenFOAM/OpenFOAM-1.6.x/tutorials/incompressible/simpleFoam/pitzDaily

About turbulentInlet: find and grep will locate these files:
/home/foam/OpenFOAM/OpenFOAM-1.6.x/src/finiteVolume/fields/fvPatchFields/derived/turbulentInlet/turbulentInletFvPatchField.H
/home/foam/OpenFOAM/OpenFOAM-1.6.x/tutorials/incompressible/pisoFoam/les/pitzDaily/0/U

It might give you a hint of what to do.

Perhaps someone else has more to say about this.

Quote:
Originally Posted by kriz View Post
Thanks for the quick reply, but, of course, I have already consulted the manual. It leaves much more questions open than it answers.

There is one table on page 133 stating some BCs of different types, however, not explaining them.

For example, "turbulentInlet" "calculates a fluctuating variable based on a scale of a mean value" and I have to specify a reference Field and a fluctuation scale. So I am as lucky as before. What is the fluctuation scale? The characteristic turbulent scale? What reference field? To what variable I can specify this BC to? Velocity?

Simple example: I want to specify a fixed value velocity BC at an inlet and a fixed value pressure BC at the outlet, what do I have to specify for pressure at the inlet and for velocity at the outlet?
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Old   May 7, 2010, 09:45
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Quote:
Originally Posted by josp View Post
For your simple example with fixedValue U and fixedValue p on inlet and outlet see:
/home/foam/OpenFOAM/OpenFOAM-1.6.x/tutorials/incompressible/simpleFoam/pitzDaily

About turbulentInlet: find and grep will locate these files:
/home/foam/OpenFOAM/OpenFOAM-1.6.x/src/finiteVolume/fields/fvPatchFields/derived/turbulentInlet/turbulentInletFvPatchField.H
/home/foam/OpenFOAM/OpenFOAM-1.6.x/tutorials/incompressible/pisoFoam/les/pitzDaily/0/U
Thanks a lot. There are still some (many) open questions for me:

- Why do I have to specify values for the k-eps wall-functions (nutWallFunction, kqRWallFunction, ...)? Just for initialising? Or do they have an effect on the wall treatment?

- Is nut=alphat/density?

- What the heck is nuTilda (same unit as nut)?

- What is R (same unit as turb.kin.en. k)?

- as far as I see it, I can set nut to "calculated" for inlet and outlet since it depends on k, eps and density only?
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Old   May 7, 2010, 21:08
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Alberto Passalacqua
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Quote:
Originally Posted by kriz View Post
Thanks a lot. There are still some (many) open questions for me:

- Why do I have to specify values for the k-eps wall-functions (nutWallFunction, kqRWallFunction, ...)? Just for initialising? Or do they have an effect on the wall treatment?

- Is nut=alphat/density?
A quick search on the Doxygen documentation shows this: http://foam.sourceforge.net/doc/Doxy...alarField.html

Quote:
- What is R (same unit as turb.kin.en. k)?
The Reynolds stress tensor.

I'd suggest you do a quick search in the doxygen manual to see how these fields are used.

Best,
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Old   May 8, 2010, 04:07
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Quote:
Originally Posted by alberto View Post
A quick search on the Doxygen documentation shows this: http://foam.sourceforge.net/doc/Doxy...alarField.html
Thanks, I didn't know the doxygen manual up to now. However, being only acquainted to matlab programming (and a little fortran from earlier years) I couldn't figure out where the value I have to specify for the boundary type "nutwallfunction" in the case\0\nut file is used in the nutWallFunctionFvPatchScalarField (being used when I use the nutwallfunction BC, I guess?).

Probably I have to look somewhere else (another subroutine?) to see what the solver is doing to or with the value I have to specify with the "nutwallfunction" BC?
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Old   May 8, 2010, 16:54
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Hi, sorry for my too quick answer :-)

- When you specify nutWallFunction, the value is required, but it does not seem to be used: set it to "uniform 0".

- nut is the kinematic turbulent viscosity: mut/rho.

- Yes, using k-eps, nut is computed based on k and epsilon, so the condition at inlets and outlets can be something like

Code:
inlet
{
   type            calculated;
   value           uniform 0;
}
again with "value" required and not used.

Best,
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