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Old   January 12, 2001, 10:48
Default Porous media
  #1
James Hampson
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I currently have a duct within which there is a grill made up of 10080 equally spaced inlets (5.72mm x 1.56mm). The duct is 632mm x 787mm x 3000mm. The grill fits flush in the center of the 3000mm duct and is 228mm thick.

CSA of Duct 497384mm2 =100%

CSA of Grill Solid 407365mm2 =81.9%

CSA of Grill Inlets 89945mm2 =18.1%

The "porosity" of the skirt assembly is thus 18.1%. Does anybody have any experience of using the porous boundary in a similar case?. Any help would be appreciated. Regards James Hampson
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Old   January 12, 2001, 13:29
Default Re: Porous media
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Evan Rosenbaum
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Sure, you just need to calculate a permeability (k) from your porosity (e) and an inertial resistance factor (C). You can calculate permeability using k = e x Dh x Dh / 32, where Dh is the hydraulic diameter. Inertial resistance can be approximately calculated using C = K / L where K is a loss coefficient (about 1.5 for a grid that is short in the direction of flow) and L is the length in the direction of flow.

Make the permeability perpendicular to the flow very small and the inertial resistance perpendicular to the flow very large, to squash any attempt to calculate flows through the solid grid portions.

All this is based on single-phase flow. You can't use porous media in FLUENT for multi-phase flow without writing UDFs.
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