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Old   September 29, 2011, 13:04
Default Correct boundary condition
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Andrea Ferrari
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Hi all,
I would like to perform this simulation using interFoam:
1) Inject a fluid in a certain domain (a box for example). My boundary conditon are (i guess standard BC for this case):

alpha1
inlet fixedValue
outlet inletOutlet

U
inlet fixedValue
outlet zeroGradient

p_rgh
inlet zeroGradient
outlet fixedValue

left and right simmetryPlane

2) After a certain period of time i would like to stop the injection and let the system relaxes. Now, i'm quite confused about which boundary condition for alpha1 U and p_rgh is better to use at the inlet. I do not want to put simply a "wall" boundary condition, because i guess it is not physical so, in your opinion, which are the correct boundary conditions to have no fluid that comes in from the inlet?

Then i have a second question. Is possibile with openFoam to switch (during the same simulation) from a boundary condition to an other?


thanks a lot

andrea
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Old   September 29, 2011, 15:07
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Nima Sam
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1) why treating the inlet in relaxation time like a wall is not physical?

2) Are you familiar with groovyBC ? to implement ur boundary easily
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Old   September 30, 2011, 03:57
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Lee Yin Jen
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Hi,
Perhaps you can extend the inlet section to have an inflow pipe/duct of reasonable length. Then during relaxation time, apply wall boundary condition in the pipe/duct which is equivalent to pipe/duct closing?
Then there will be reasonable interaction between the domain of interest and the inlet section during relaxation.
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Old   September 30, 2011, 04:06
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Andrea Ferrari
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Hi, and thanks for the answer.
1)Because physically there isn't a wall (if you think for example an experiment). simply i want no flow that comes in. Put a "wall" boundary condition is the only choise i have? Something like:

alpha1: zeroGradient
U: fixedValue (0 0 0)
p_rgh: zeroGradient or buoyantyPressure ??

2)no, i'm not familiar with groovyBC, but if you are saying that you can easily implement a sort of "switching BC", i wiil give a look for sure.

Best

andrea
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Old   September 30, 2011, 04:25
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Andrea Ferrari
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Another idea could be to impose a "correct" pressure gradient between the inlet and the outlet and then to simulate until nothing moves (until there is no flow from the inlet). Is possibile with OF?

andrea
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Old   September 30, 2011, 06:02
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Nima Sam
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Quote:
Originally Posted by Andrea_85 View Post
Hi, and thanks for the answer.
1)Because physically there isn't a wall (if you think for example an experiment). simply i want no flow that comes in. Put a "wall" boundary condition is the only choise i have? Something like:

alpha1: zeroGradient
U: fixedValue (0 0 0)
p_rgh: zeroGradient or buoyantyPressure ??
i feel you can consider for U zeroGradient or outletInlet condition

Quote:
2)no, i'm not familiar with groovyBC, but if you are saying that you can easily implement a sort of "switching BC", i wiil give a look for sure.
look in wiki and froum you can find many examples using it
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Old   September 30, 2011, 09:34
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Andrea Ferrari
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Hi,
i found the "timeVaryingUniformFixedValue" BC, which is probably what i was looking for (it seems easier than groovyBC). I set
alpha1 inlet inletOutlet, inletValue 1, value 1
outlet inletOutlet , inletValue 0, value 0

p_rgh inlet zeroGradient
outlet fixedValue

U inlet timeVaryingUniformFixedValue
outlet zeroGradient

and then i used the "ramp" file to switch between fixed velocity and zero velocity at the inlet. The inletOutlet BC at the inlet for alpha1 should ensure fixedValue =1 when the velocity is non-zero and zeroGradient when the velocity is zero. It seems to work.
thanks again

andrea
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