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Assigning anisotropic permeability in ANSYS CFX

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Old   September 9, 2016, 04:21
Default Assigning anisotropic permeability in ANSYS CFX
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willsen
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Hi Everyone!

I am trying to model resin flow through a textile unit cell as can be referred to the attached picture. From the picture it is clear that the fluid will flow at inter-tow channel (the gap BETWEEN the fibrous yarns). Furthermore there will also be flow inside the yarns (because each yarn consists of thousands of fibers).

To model the flow through this unit cell two domains shall be defined: fluid domain (inter-tow channel) and porous domain (the tows).

My question is, is it possible to assign permeability tensor in ANSYS CFX? Furthermore, is there a trick to transform this permeability tensor according the direction of the tow?

Thank you very much!
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Old   September 9, 2016, 07:17
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Glenn Horrocks
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Sounds like you need the directional loss porous model. Have a look in the documentation for details.
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Old   September 9, 2016, 21:11
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Hi,

Thank you very much for your kind reply. Are you referring to the 3 types of momentum sources (isotropic loss model, directional loss model, and general momentum sources)?
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Old   September 9, 2016, 21:37
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Yes, that is correct.

Or are you talking about the area porosity tensor? To quote from the documentation: "ANSYS CFX presently allows only K to be isotropic". So you cannot use an anisotropic area porosity tensor.

So you can specify the resistance to be in any direction you like, but the area porosity tensor must be isotropic.

There may be beta features to get around this. I am not familiar with them so cannot help you there. Others on the forum may be, or you can ask ANSYS support.
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Old   September 9, 2016, 22:06
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Hi,

Once again thank you for your reply. So the way I would like to approach this is by first determining the permeability tensor inside the tows through an analytical model (which I have already calculated from the information of the porosity inside the tows and the fibre radius).

To model the flow inside the tows, I would like to input this permeability tensor inside the yarn accordingly depending on the principal direction of the tows and obtain the velocity inside the tows in term of superficial velocity. So I don't really need to input this porosity information as it has already been taken into account when I calculated the tows' permeability analytically.

To my understanding, ANSYS CFX allows me to obtain this superficial velocity field inside the tows by simply adding momentum loss term to the governing flow equation (without altering the equations like in the full porous model). According to the documentation (I screenshot the relevant section from Solver Theory Guide), this is done by defining the porous body as FLUID DOMAIN. However, ANSYS CFX only allows me to add these directional porous losses terms in the POROUS DOMAIN under the porosity setting tab. Do you think there is a miscommunication from the documentation?

Furthermore, the momentum loss term requires both PERMEABILITY and QUADRATIC LOSS COEFFICIENT. How do we calculate this quadratic loss coefficient? I have never come across any literature in the field of textile permeability that includes this quadratic loss coefficient in their numerical model.

THANK YOU. Really in desperate need for advice.
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Old   September 10, 2016, 07:58
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I am not an expert on porous models in CFX. Hopefully others in the forum can answer you question.
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Old   September 10, 2016, 17:40
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Thank you very much for your help. I shall report my question to the forum so that other people in the forum don't think that the problem has been resolved. Appreciate your help once again
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