# wall functions

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 November 14, 2009, 13:26 wall functions #1 Senior Member   karine Join Date: Nov 2009 Posts: 158 Rep Power: 9 Hello everybody i have a question about wall functions in Fluent: 1- Is wall function applied only for the first near wall cell, or for the whole boundary layer??? 2- To calculate the velociy values using wall functions, we need to have the friction velocities. Anyone can tell me how Fluent calculate the friction velocity? Thanks

 November 14, 2009, 15:28 #2 Member   Join Date: Oct 2009 Location: Italy Posts: 88 Rep Power: 10 i think that you know becouse don't see the velocity profile near a wall with your simulation. this depend on the mesh that aren't sufficiently accurete, so i'm sorry but you take gambit and near the wall you reduce a size of mesh. i understend your question? i hope useful bye p.s. for how cumpute the value, fluent use the differential equations and trasform it in algebric equation approsimate that function with a difference (as such as the definition of derivative in mathematics) and the residual is the error that fluent introduced in this operation.

 November 15, 2009, 16:16 #3 New Member   ARSLAN Join Date: Nov 2009 Posts: 5 Rep Power: 9 1. B.C. only for the first cell, in the boundary layer Fluent calculate according to 'wall functions' about second question i not understand what u want to compute and what you meen by "friction velocity"

 November 16, 2009, 05:42 #4 Senior Member   karine Join Date: Nov 2009 Posts: 158 Rep Power: 9 Thank u comrade u responded to my second question too friction velocity is uf (u+=u/uf) regards

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