Dear Support and Users,
I have a question regarding the boundary layer thickness: is there any way to have an idea of its value after running Code_Saturne (maybe by using some values in the listing file)?
Regards,
Stéphane
Hello,
If you activate postprocessing of boundary fields (ichrbo = 1 in usini1.f90, or simpler, checking the appropriate box under post-processing options in the GUI), you will obtain the Y+ field at boundary cell centers on the boundary mesh (whether using EnSight, MDE, orCGNS output), so if you combine it with the boundary cell thickness, you may have an estimate of the boundary layer thickness).
Best regards,
Yvan
Hello,
Thanks you for your answer. When you say “combine”, do you mean multiply?
But anyway, I don’t understand how you can estimate the boundary layer thickness knowing y+ and the cell thickness.
Best Regards,
Stéphane
Hello Stéphane,
The y+ value will give you to which distance you are (dimension-less speaking) from the wall, you can then have a clue of where the first off-wall cell is in the boundary layer.
Usually, one defines the boundary layer thickness as the distance from the wall where the velocity is 99% of the free-stream velocity. This isn’t straightforward to compute it… You can also compute the momentum thickness or the displacement thickness, see Wikipedia for example.
Do you have a precise definition of the boundary layer thickness you want to plot/compute?
David
A solution that can be used is to follow these steps:
- draw lines perpendicular to the surface (profile)
- export the stream-wise velocity profile along the lines
- extract the boundary layer thickness using 99% of the stream-wise velocity at each profile
This is what I would do to easily compute the boundary layer thickness. But if anyone as a better option, feel free to post it
I had this solution in mind actually, but I was looking for something more straightforward.
But thank you anyway, I will try this solution!
Stéphane