# y+ calculations

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 May 24, 2002, 08:14 y+ calculations #1 henry Guest   Posts: n/a hi Does any one now how to calculate the distance a near wall cell should be ,if I know the flow details, and I want to maintain the y+ between 30 and 100 as per CFX. please help. henry

 May 24, 2002, 08:41 Re: y+ calculations #2 cfd guy Guest   Posts: n/a Hi, In TASCflow and CFX-5 the yplus values at walls are stored by default in the results file. In CFX-4 you only need to add three lines in your command file to see these values under the post-processor. Regards, cfd guy

 May 24, 2002, 10:36 Re: y+ calculations #3 Robin Guest   Posts: n/a Actually, TASCflow will only output yplus values if the BCINFO = t flag is set. As an initial guess before you run for the first time, there are correlations for boundary layer development over a flat plate. Look up section 4.4.4 of the TASCflow doc for details, or Mathmatical Models and Solution Algorithms > Modelling Flow Near the Wall > Guidelines for Grid Generation section of the CFX-5.5 doc (see math_models.pdf). Regards, Robin

 May 27, 2002, 08:45 Re: y+ calculations #4 Michael Bo Guest   Posts: n/a

 May 27, 2002, 08:47 Re: y+ calculations #5 henry Guest   Posts: n/a hi Thanks for the info, but I wanted the formula to calculate the Y+ from the flow variables like Re ,etc henry

 May 27, 2002, 09:01 Re: y+ calculations #6 henry Guest   Posts: n/a hi Could some one give the formula please. joe

 May 28, 2002, 08:41 Re: y+ calculations #7 Patrice Jaumouillie Guest   Posts: n/a y+, the dimensionless distance from the wall, can be calculated from the formula : y+=(rho.u*.y)/mu where rho and mu are respectively the density and the dinamic viscosity of the fluid, y is the distance from the wall and u* is the shear velocity. The three regions are (may vary from different authors) : The viscous sublayer 0

 May 30, 2002, 16:43 Re: y+ calculations #8 Robin Guest   Posts: n/a Have a look at the documentation, it's in there. Robin

 June 3, 2002, 03:38 Re: y+ calculations #9 henry Guest   Posts: n/a hi Patrice thanks soo much , do you know how the shear velocity is calculated. thanks again joseph

 June 27, 2002, 20:48 Re: y+ calculations #10 Min-Hua Wang Guest   Posts: n/a Hello, All: I am very interested in this topic. I am using CFD-4 now. I am trying to export y+ data from the simulation. It seems to me that one can obtain some meanfull y+ values as the wall is still (not moving). Do I still expect the correct y+ values from the simulation with a standard wall function if the wall is in moving ( bassically the wall is rotating in my study)? Min-Hua Wang

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