wall functions

thecfduser · November 14, 2009, 13:26

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

bob12 · November 14, 2009, 15:28

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.

arslan · November 15, 2009, 16:16

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"

thecfduser · November 16, 2009, 05:42

Thank u comrade
u responded to my second question too

friction velocity is uf (u+=u/uf)
regards

November 14, 2009, 13:26	wall functions	#1
thecfduser Senior Member karine Join Date: Nov 2009 Posts: 158 Rep Power: 17	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

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November 14, 2009, 15:28		#2
bob12 Member Join Date: Oct 2009 Location: Italy Posts: 88 Rep Power: 17	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
arslan New Member ARSLAN Join Date: Nov 2009 Posts: 5 Rep Power: 17	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
thecfduser Senior Member karine Join Date: Nov 2009 Posts: 158 Rep Power: 17	Thank u comrade u responded to my second question too friction velocity is uf (u+=u/uf) regards