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How to define the number of cells within a boundary layer(fluent/cfdpost) |
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March 20, 2015, 05:59 |
How to define the number of cells within a boundary layer(fluent/cfdpost)
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#1 |
Member
Join Date: Jan 2015
Location: United Kingdom
Posts: 53
Rep Power: 11 |
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 |
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March 22, 2015, 19:50 |
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#2 |
Senior Member
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,677
Rep Power: 66 |
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. |
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March 25, 2015, 03:15 |
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#3 |
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wanghuo
Join Date: Aug 2014
Posts: 89
Rep Power: 11 |
How to calculate the Y+ for the all ten cells (or just the tenth cell) ?Thank you very much !
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March 25, 2015, 13:19 |
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#4 |
New Member
Daniel Wilde
Join Date: Jan 2014
Posts: 21
Rep Power: 12 |
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 Last edited by QCFD; March 26, 2015 at 07:53. Reason: add more info |
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March 25, 2015, 17:39 |
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#5 |
New Member
anonymous
Join Date: Mar 2015
Posts: 25
Rep Power: 11 |
You can define the number of boundary layers within your mesh in design modeler mesh.
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October 22, 2015, 02:10 |
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#6 | |
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N B Khan
Join Date: Jan 2014
Posts: 39
Rep Power: 12 |
Quote:
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 |
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