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Setting different diffusivities for two domains (fluid+porous)

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Old   November 25, 2014, 13:14
Default Setting different diffusivities for two domains (fluid+porous)
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Leonardo
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Hi there,

I need some help setting up a CEL expression to define different values of kinematic diffusivity for two different domains: a fluid and a porous domain. I'm aware you can use the inside() function, but I'm not sure how to write it. I tried the script below but it didn't work.

1.58e-5 [cm^2 s^-1] * inside()@flow;
0.46*1.58e-5 [cm^2 s^-1] * inside()@porous

Thanks in advance.
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Old   November 25, 2014, 14:45
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I assume you are defining the Kinematic Diffusivity parameter for an Additional Variable, or mass fraction Component

Kinematic Diffusivity = 1.58e-5 [cm^2 s^-1] * ( inside()@flow + 0.46 * inside()@porous)

That is all you need to do.

I wonder what the 0.46 means. It is not the volume porosity, is it ?
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Old   November 25, 2014, 14:48
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Quote:
Originally Posted by Opaque View Post
I assume you are defining the Kinematic Diffusivity parameter for an Additional Variable, or mass fraction Component

Kinematic Diffusivity = 1.58e-5 [cm^2 s^-1] * ( inside()@flow + 0.46 * inside()@porous)

That is all you need to do.

I wonder what the 0.46 means. It is not the volume porosity, is it ?
Thanks a lot, I'll try that.

What is the meaning of the asterisk symbol in the CEL syntax? I did a quick check on the documentation and couldn't find much about syntax.

And no, it's just the "correction" factor for the permeability at the porous media.
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Old   November 25, 2014, 15:26
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* is for multiplication between two terms in the expression.

Not sure I catch on the "correction factor" for the permeability. There is no permeability in the diffusion terms of the transport equations I have seen. I have only seen the permeability in the drag force term in the momentum equation.. Did you mean porosity ?

The only time I have seen permeability into a transport equation is when Darcy's law is substituted into the continuity equation, and a pure diffusion equation for Pressure is obtained. Is that what you are solving for ?
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Old   November 25, 2014, 15:30
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Quote:
Originally Posted by Opaque View Post
* is for multiplication between two terms in the expression.

Not sure I catch on the "correction factor" for the permeability. There is no permeability in the diffusion terms of the transport equations I have seen. I have only seen the permeability in the drag force term in the momentum equation.. Did you mean porosity ?

The only time I have seen permeability into a transport equation is when Darcy's law is substituted into the continuity equation, and a pure diffusion equation for Pressure is obtained. Is that what you are solving for ?
Sorry about that, I meant diffusivity.
According to the paper I'm basing my simulations on, they estimate the effective diffusivity of ethanol in the porous media using this factor, which indeed happens to include the porosity:

D_eff = (porosity)^1.5*D
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