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icoFoam >> density >> kinematic viscosity for air 20C

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Old   November 30, 2009, 04:19
Default icoFoam >> density >> kinematic viscosity for air 20C
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Markus Golbs Hamm AG
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Hello,

I want solve a problem whis air by 20C in profile whis turbulent flow and icoFoam. Where can i set the density of air and the kinematic viscosity? Is the k/e-Modell in icoFoam use for turbulent flow?

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Old   December 1, 2009, 07:00
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Gijsbert Wierink
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Hi Markus,

You can set nu in constant/transportProperties.
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Old   December 1, 2009, 10:23
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Hello,

thank's! I have a problem, because icoPipe is only for laminar flow. I need turbulent flow. Also I must use simplefoam. The are any parameters to set:

# Field Patch Field Type
U ......................
p ......................
k ......................
epsilon ......................
R .....................
nuTilda .....................

Which physical properties to allocate U, p, k, epsilon, R, nuTilda and which physical quantity?

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Old   December 1, 2009, 13:50
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Hi Markus,

Use simpleFoam if you want steady-state, or pisoFoam for transient flow.

I would recommend you to start by looking in the OpenFOAM user guide, there you have a couple of tutorials on setting up turbulent cases.

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Old   December 2, 2009, 10:52
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Hello,

thanks for the informations. In the openFoam userGuide are importent dokus. I have solve a modell whis icoFoam, linear flow. This works well. The same modell I would like the same mesh solve whis simpleFoam.

Is pisoFoam under 1.4.1 not available?

Where can I set the density of flow medium?

The definition of boundary in simpleFoam are likewise icoFoam.
# the wall surfaces are set to wall >> the paremeter from U, p...nuTilda are constants? When no, where can I manage this parameter, in asci File?
# the Flow input surfaces are set to inlet >> the paremeter from U, p...nuTilda are also constants?
# the flow output surfaces are set to outlet. >> the paremeter from U, p...nuTilda are also constants?

Under point Fields (simpleFoam) are the parameter U, p, k, epsillon, R, nuTilda.

# Is U the flow velocity in X,Y and Z direction?
# Is p the pressure in SI Unit?
# What is k - the thermal conductivity or k=1/2(Ux...)?
# What is epsillon for a physical value epsillon=C...^0.75.../l?
# What is R for a physical value - Reynolds Stress?
# What is nuTilda for a physical value?

About informations I'm very happy!

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Old   December 2, 2009, 12:28
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Hi,

In 1.4.1, pisoFoam=turbFoam.

You don't need to set the density for an incompressible fluid, you just set the kinematic viscosity=viscosity/density in the constant/transportProperties of your case.

Regarding the boundary conditions and initial fields, you can look in the tutorials available on how to set them (cd $FOAM_TUTORIALS && ls).

The answer to all your remaining questions are in the User Guide, I suggest you to study it in detail.

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Old   December 2, 2009, 12:37
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Hi Markus,

Here some short answers. I think pisoFoam in OF-1.6 is like turbFoam in OF-1.4.1, an incompressible transient solver.

You can set U, p, etc in 0/.

k is the turbulent kinetic energy k = 1/2 (u')^2

epsilon is the dissipation rate epsilon = C_mu^0.75 * k^1.5 / L, where C_mu is usually 0.09 and L is, say, 20% of channel width.
This stuff is explained in section 2.1.8.1 of the user guide.

The dimensions of p depend on the solver, but they are SI anyways: [kg m s T n A cd], so [0 1 -2 0 0 0 0] means m/s^2.

Hope this helps!
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Old   December 2, 2009, 12:39
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Oh yeah, forgot, you can set the density in constant/transportProperties by changing the kinematic viscosity nu (which is the dynamic viscosity mu divide by density) ...
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Old   December 4, 2009, 02:25
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Hello,

thanks for the many Informations. I have a look in the userGuide.. but not all my questions are answered.

When I create a modell "90 pipe" -turbulent air, whis wall, one input 10m/s y-Direction, and 100 Pa relativ, one output whis 0 Pa relativ medium air 20C and I searching "distribution of pressure" and "distribution of velocity" in the "90pipe" what must I set leastwise in turbFoam?

The output after solving "pressure" are "static pressure" or "velocity head" or "velocity head and static pressure"?

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Old   February 11, 2010, 05:00
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Hello,

....k is the turbulent kinetic energy k = 1/2 (u')^2

epsilon is the dissipation rate epsilon = C_mu^0.75 * k^1.5 / L, where C_mu is usually 0.09 and L is, say, 20% of channel width....

Is k and epsilon only to set in internalField, or also in inlet and outlet faces?

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Old   February 13, 2010, 02:50
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Hi Markus,

You need to set k and epsilon at the inlet, outlet, as well as for the internalField. You could set k and epsilon according to the equations above and then the internal field to 0 or something small (e.g. 1% of inlet value).
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Last edited by gwierink; February 13, 2010 at 02:51. Reason: typo
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Old   February 15, 2010, 10:09
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Hello,

thanks for the informations. My mistake was setting "0" in the internal field of k and epsilon.

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