How to define the number of cells within a boundary layer(fluent/cfdpost)
 

Dear all,

I am wondering how do I define my number of cells in the boundary layer given that I know my y+ which is the distance of first cell away from the wall.
Let say I got y+ of 0.5 to 20 and for my region of interests(rotating surface) my y+ is 5 (therefore I use enhanced wall treatment). However, according to theory, I need to have 10 cells within the viscous sublayer. Y+ 0 to 5? or approx 0 to 10?

Can someone advice me on how to know whether my cells are within the BL.

I know that for first cell let say 0.1 mm next one is 0.12 (Growth ratio of 1.2) and 0.144 mm etc. But I am curious how I know whether it is still within the buffer layer before it escape to outer layer.

Thanks

Regards,
J

y+ is a generalized coordinate system, it is not limited to only the first cell at the wall. This is common misconception, some people say y+ when they actually mean y+ of wall adjacent cell. y+ can be calculated for any cell, not just the wall adjacent cells. That is why some refer to the first cell y+ value as the wall y+.


Use this procedure and calculate the Y+ for the all ten cells (or just the tenth cell) and check if it's still Y+ < 5, Y+<10 or whatever criteria you like to be using.

How to calculate the Y+ for the all ten cells (or just the tenth cell) ?Thank you very much !

Instead of worrying about y+ for your first 10 cells, look at the turbulence Reynolds number for those cells.. I typically check that I have several elements in the region below Turb Re = 200.

What I mean is: worry about your 1st element y+, your growth ratio, and the number of elements below turb Re=200

You can define the number of boundary layers within your mesh in design modeler mesh.

Sir, I have one question
I am analyzing the flow around circular cylinder(dia=0.1m, Vel=0.5275m/s, dyn visc=1.6e-5kg/m/s, density=1.185kg/m^3)
I calculated first cell height for y+ value of 1 which is 0.3mm.
Now in order to ensure the 15nodes with in BL or in order to ensure 20 layers to cover BL..what setting should i do in INFLATION option of meshing??
In inflation option, should we use first layer thickness option and input the first cell height value at "First layer hight value??
Thanks in advance