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-   -   how can I increase Y-plus in 2D geometry (http://www.cfd-online.com/Forums/fluent/46674-how-can-i-increase-y-plus-2d-geometry.html)

rb November 26, 2007 15:46

how can I increase Y-plus in 2D geometry
 
Hi I am simulating 2D geometry I saw my y+ value very law can anyone guide me how can i increase it?

rb


Kasper November 27, 2007 05:42

Re: how can I increase Y-plus in 2D geometry
 
Take a look at this to understand y+: http://www.cfd-online.com/Wiki/Dimen..._wall_distance

Y+ is the non-dimensional wall distance. The formula y+ = u(star) * y / kin_visk, says it all for you.

If you wan't to increase y+ value then make the center of you first cell further from the wall. Or change the kinematic viskosity.

The value of y+ in the first cell should be controlled in regard to what you are modelling. Take a search on y+ in forum and you will find loads of information.

BR Kasper

rb November 27, 2007 06:28

Re: how can I increase Y-plus in 2D geometry
 
Hi thanks for the information you sent. I saw the formula for estimating the desire grid distance but it was mentioned for flow a flow over a flat plate? is it work for the case of pipe flow and how much the value of Ref. length in this case for y+=41 & diameter=77.92 mm?

rb

Kasper November 28, 2007 03:55

Re: how can I increase Y-plus in 2D geometry
 
I think the diameter could be the reference length, but I'm not sure. Use the grid spacing calculator: http://geolab.larc.nasa.gov/APPS/YPlus/#TOTAL

and insert y+=41 ref.length=0.07792m and your Re no.

But why are you using y+=41?

BR Kaspeer


rb November 30, 2007 10:53

Re: how can I increase Y-plus in 2D geometry
 
because I need to use the non-equilibrium wall function as wall treatment so I want set y+ over 30? Do you have another suggestions?

rb


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