# UDF for wall boundary condition

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 October 21, 2009, 03:29 UDF for wall boundary condition #1 New Member   Suren L S Join Date: Oct 2009 Posts: 2 Rep Power: 0 Greetings. I am in need of some technical advice here. I am trying to simulate a cavity-filling flow. My geometry (2D) is a simple rectangle, and the two longest edges are the top and bottom wall. The other two edges are the 'velocity inlet' and 'pressure outlet' respectively, and the flow is from left to right. The cavity is initially filled with air and a viscous polymer enters via the velocity inlet at a fixed velocity. I am using a transient, segregated, laminar solver, with the VOF scheme to model the filling process. In addition I am also solving the energy equation and using a power law model to model the viscosity of the polymer. Right now, the solution converges, and the results are decent except for one particular problem. The layer closest to the wall remains as air and the polymer does not displace it at a reasonable rate - this results in a rather skewed flow front profile. I have read literature on this problem and some researchers have overcome this by using two sets of wall-slip conditions. No-slip for the viscous polymer and traction-free for the air. I am trying to do this as well, but am having quite a bit of trouble implementing this as a UDF. I would appreciate any help. Thanks. Suren

 October 23, 2009, 08:40 #2 Senior Member   Max Join Date: Mar 2009 Posts: 133 Rep Power: 11 Hello Suren, i think a no-slip BC is correct for both phases and should not be altered in any way. I would suggest to define surface tension and an appropriate wall contact angle to make your polymer the wetting phase. This should displace air from the adjacent wall cells effectively and in a physically sensible way. cheers

 October 28, 2009, 04:32 #3 New Member   Suren L S Join Date: Oct 2009 Posts: 2 Rep Power: 0 thanks a bunch for your suggestion. It should definitely be helpful to my work. Cheers

 Tags udf, uds, walls boundary conditions