# UDF to Access Wall Normal Concentration Gradient

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 May 6, 2009, 14:10 UDF to Access Wall Normal Concentration Gradient #1 Member   Daniel Tanner Join Date: Apr 2009 Posts: 54 Rep Power: 18 I want to calculate and store the wall normal concentration gradient at my wall boundary. I have compiled my udf and it works correctly. However, I have some questions, below is a section of my udf for reference. ******************************************* /* Get Connectivity Data */ BOUNDARY_FACE_GEOMETRY(f,t,A,ds,es,A_by_es,dr0); /* Calculate Wall Normal Inter-centroid distance (dn)*/ dn = NV_DOT(A, (es*ds))/NV_MAG(A); /* Calculate Wall Normal Concentration Gradient*/ C_UDMI(c0, t0, 1) = ((F_YI(f,j,0)*F_R(f,j))-(C_YI(c0, t0,0)*C_R(c0,t0)))/dn; ******************************************* 1) I am unsure (though the difference is probably quite small) if it is better to use the inter-centroid distance in the wall normal direction ("dn" - as defined above) or "ds" as returned by the BOUNDARY_FACE_GEOMETRY macro to calculate the wall normal gradient (i.e., dpsi/dn or dpsi/ds). 2) To establish the concentration gradient is mass_fraction*density the correct term to use: F_YI(f,j,0)*F_R(f,j) - C_YI(c0, t0,0)*C_R(c0,t0) 3) I store these values at the centres of the cells (using C_UDMI) adjacent to the wall. Will this cause an error when contours of concentration at the wall are displayed in fluent, i.e., this would require the interpolation of the cell-centred values onto the wall and hence they would be different. Thanks...

 May 18, 2012, 10:35 #2 New Member   moon Join Date: Feb 2012 Posts: 26 Rep Power: 14 more informations please , i'm verry interrested thx

 May 21, 2012, 04:23 #3 Member   Daniel Tanner Join Date: Apr 2009 Posts: 54 Rep Power: 18 What questions do you have? If you have a UDF you are trying to create post it and I'll have a look.

 May 21, 2012, 11:14 #4 New Member   moon Join Date: Feb 2012 Posts: 26 Rep Power: 14 Yes Mr daniel , may you send me this udf please . thank you a lot

 February 18, 2015, 14:35 Help with the same problem #5 New Member   Nandish Join Date: Sep 2012 Posts: 5 Rep Power: 13 Could you please give more detail on your UDF.