Decreasing surface roughness in a pipe

pat

Hello,

Here is my problem: I want to study the turbulent flow in a 3D circular pipe with FLUENT. I have boundaries taken as periodic for the inlet/outlet and walls on the pipe surface. I use the Reynolds-stress model. I want to add a surface roughness on the wall, that decreases from the bottom of the pipe to the top (along the circumference). How can I do that? I should probably create a UDF, but I am rather novice in this field. Any idea? Is there any Fluent tutorial I should refer to?

Many thanks. Pat.