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Old   September 24, 2012, 10:10
Default No turbulence generation in a porous domain
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siw
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Hi,

I'm modelling (steady RANS SST) a porous domain representing an air filter. On each end of the porous domain is a fluid domain for the inlet and outlet airflows - e.g. CFX catalytic converter tutorial.

In reality the filter consists of small random pathways which the air passes through, so any turbulent structures are eliminated by the filter media. Then downstream of the filter the air can then develop any new turbulent sturctures. I guess this would be similar to modelling a turbulence screen that can be found in wind tunnels.

How can I model the porous domain with turbulence removal? I've tried setting: Porous Domain > Fluid Models > Turbulence > Advanced Turbulence Control > Eddy Viscosity > Value = 0 Pa s. But then CFX copied this value to the two fluid domains, which is not right.

My next option is to create a turbulence sink via a subdomain in the porous domain. However, this option is requiring a source and a source coefficient. Do I just set these to 0 in the porous domain? Or is there another way to do this?

Thanks
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Old   September 24, 2012, 21:52
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Glenn Horrocks
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I would use a source term. I am not sure whether the best way would be to specify zero turbulent energy in the porous region - you might not be able to use zero, you might need to set a low value. Alternately you could set the turbulence dissipation to be very high (if using the k-e turbulence model) and then turbulence will naturally damp out very quickly.
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Old   September 25, 2012, 05:00
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siw
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As mentioned in the top of the first post I'm using the SST model.

I've set a subdomain within the porous domain and set the turbulent kinetic energy source to zero. Is that what you meant?
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Old   September 25, 2012, 08:10
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Yes, that is what I meant. But I am not sure that the turbulence model will gracefully handle zero turbulent kinetic energy - you might need to set it to a small finite number. But if it runs OK at zero then no problems.
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