[luca007]

hello. please im very new in cfd and i need your help for calculation the both partamatres
1 firest layer height
2 maximum layer
best regads

[LuckyTran]

First you need to pick a desired y+. This is usually something like 1,2,5, 30, 100, etc.

Is it external flow or internal flow?

If external, check out the following tools:
https://www.cfd-online.com/Tools/yplus.php
https://geolab.larc.nasa.gov/APPS/YPlus/

For internal, y+=1 is around 1% of the duct radius.

[luca007]

hello thank you LuckyTran for you reply. son im woking for stepped spilways so its externel flow but i dont understant whish value i need for y+
my qustion is how i can know my y+
second how i can used inflation ? which value i need in first layer? height and maximum layer? and groth rate ?

best regards

[LuckyTran]

Honestly just mesh whatever and get a simulation going. After you have gotten a result, see if it makes sense. Don't be afraid to do the wrong thing and miss out on learning in the process.

Originally Posted by luca007

my qustion is how i can know my y+

You can't. You only know what the y+ is after you have solved the problem. All you can do is take an educated guess. That is, you hope that your 1st cell layer height ends up at approximately a certain y+ value.

The desired y+ depends on your modelling approach. I.e. laminar or turbulent. If turbulent then what turbulence model you are using and then what wall treatment you want to use. You want to choose an approach grid size that is consistent with the model that you employ. But really, it is a user choice. You can pick anything, but your result may and probably will affected.

Any number between 1 and 1.5 is reasonable for the growth rate. Small numbers gives more dense grids (which some people like for certain reasons) and large numbers gives fewer cells (which many people like). It's up to you. But unless you have a specific reason to want to change the growth rate, maybe you can just leave it alone.

[luca007]

so i used k-eps RNG and standar wall traitement so whats value of + should be in my results ?
is my results of y+ wrrong whats the solution

best regards