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How to set up a porous region?

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Old   August 13, 2011, 18:42
Default How to set up a porous region?
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Hey guys,

I have a starightener which is made of cylinder tubes. The porosity is 70%. So I treat it as a porous media. But I have some questions.

1.I wonder how to set up those parameters, like porous inertial and viscous resistance. Just follow the equation in the turorial?

2.How about the turbulence length scale? I found that usually it's 7% of the diameter if it's a tube. Is that correct?

3.Do I need to specify the mass and momentum source option? If yes, the mass source is just the mass flow rate in the inlet?

4.I also notice that there is node named AXIS, how to specify that? The flow direction into the porous media or using the default one?

5. How about the delta P/L? DO I need to specify it and where?

6. What's the superficial velocity? (m/s)

7. I only need to specify parameters within the region part, correct? Or I also need some initial value for the porous region, like pressure and mass flow rate?

I appreciate any help!
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Old   August 14, 2011, 18:28
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anyone can help any of them? Thanks !!!
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Old   August 14, 2011, 22:01
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you need to know the character of your porous material to work out the required coefs - normally people have pressure vs velocity data from experiments which they then graph and fit an equation to and thus have the coefs. Most porous flow is laminar so turbulence is not important. Only need sources if you want to add or subtract mass etc within the porous region - like any region - no different. Superficial vel is a typical vel. Initial conditions advice is the same as any other region in your sim - can help convergence if you have/can provide better information otherwise not an issue.
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Old   August 21, 2011, 07:59
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Additionally to the AXIS parameter: You need to specify the axis in porous media properties, as it defines the axis in which every tensor component should be taken into account. You will find a good explanation when searching for "orthotropic viscous resistance" in the user guide.
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Old   September 29, 2011, 01:50
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dp/Thickness = alpha U + Beta U^2.

this is the forumla for porous media coefficient calculations.
if you know the pressure drop and know the thickness of the actual straightener, then you can calculate these values and input them into the region. I have done this many time.
I ll be glad to help, but need to see the geometry.
I ll send you my work email, if you I can take a look.

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