# How can I specify different permeability?

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 February 25, 2003, 13:54 How can I specify different permeability? #1 Ahmed Khattab Guest   Posts: n/a In my case, which is a rectilinear flow in a mold, filled with carbon fiber, I want to change the permeability near the mold wall so the flow front will be faster near the edge (higher permeability near the edgs). So how can I specify different permeability to FLUENT?

 March 2, 2003, 22:39 Re: How can I specify different permeability? #2 Murali Guest   Posts: n/a I think you should use the Macro DEFINE_PROPERTY Murali

 March 2, 2003, 23:27 Re: How can I specify different permeability? #3 Ahmed Khattb Guest   Posts: n/a Thanks for your help. I'm new user to FLUENT, so if you please can you help me with more details

 March 4, 2003, 18:50 Re: How can I specify different permeability? #4 Murali Guest   Posts: n/a Since you say that you are new to UDFs, I suggest you peruse the UDF manual which will help you greatly. But let me provide you some tips which I am familiar with: (1) Since permeability is a 'property' or a number just lilke say diffusivity or viscosity, it can be calculated through a UDF and be passed to FLUENT while running. (2) The way to do is to use by accessing DEFINE_PROPERTY macro. (3) If you are completely unfamiliar with UDFs, then these are the preliminary concepts: cell = computational cell face = face of the cell thread = a collection of faces or cells but not both (4) Since the 'property' of the material is a 'cell value' dependent upon the 'material' of the cell, the DEFINE_PROPERTY Macro would compute your required value and send it to the FLUENT solver while running (5) Section 4.3.13 of UDF manual of FLUENT 6 gives you this information. DEFINE_PROPERTY(cell_permeability, c, t) { real perm; real x[ND_ND]; C_CENTROID(x,c,t); if (x[0] == 1) { perm = 5; } else { perm = 10; } return perm; } The above example I think should tell you how this works. It first obtains the centroidal information and stores in x, a real array. x[0] has the x co-ordinate and this value is checked. IF x[0] = 1, then the value of permeability to be specified is 5 or else 10. (6) Once you have written this udf and compiled properly as given in chapter 8 of the UDF manual, you shall see the UDF name appearing in the drop-down list. Select cell_permeability in the appropriate place. (7) Lastly, all these have been written under the assumption that you have to specify permeability as just a number (and not a relation) Hope this helps Murali

 March 10, 2003, 17:39 Re: How can I specify different permeability? #5 Ahmed Khattab Guest   Posts: n/a I'm working to fully understand the UDF manual, but in the example defining the viscosity, and also other examples, there is a drop-down list to select UDF from it, which is not the case for permeability, is that a problem? Thanks.

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