[hallabong]

Hi, newbie here. please forgive my ignorance.

I'm trying to model an airway. Below is my conditions:
standard k-epsilon
velocity-inlet and pressure-outlet
no slip standard wall function

I made a hybrid mesh with prism layer near wall and tetrahedral in the center.
From it, I get reasonable result. yet the y+ value was around 1.
I was told that I should have y+ value near 100 for k-e.

to increase y+, i need to increase the initial height of prism layer near wall.
But this leads to intuitively wrong mesh.

What am I doing wrong here and what should i do? Why can't i just have y+ around 1?

reasonable mesh:
https://imgur.com/gallery/UlHaD0u
reasonable result:
https://imgur.com/gallery/yvR3m3Q


increased initial height:
https://imgur.com/a/SK5FppL

[LuckyTran]

You can have a wall y+ of around 1 and it is preferred.


You should ask the ghost that told you 100 why 100.

[hallabong]

thank you for your reply.

When I asked the guy who told me that y+ should be around 100, he just told me that it was from a user guide.

I read the user guide, which i couldn't find that. I did saw that y+ should be above 30 ~ 300when using wall function. So i think that's what he meant by.

But i decided to just lower the y+ below 1 and to directly solve the boundary layer.

Thank you for your help!

[telegrampay.eth]

it depends on your turbulence model and wall functions, in some wall functions y+ should not fall in the logartimic boundary lyer zone