y+ calculations
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 
Re: y+ calculations
Hi,
In TASCflow and CFX5 the yplus values at walls are stored by default in the results file. In CFX4 you only need to add three lines in your command file to see these values under the postprocessor. Regards, cfd guy 
Re: y+ calculations
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 CFX5.5 doc (see math_models.pdf). Regards, Robin 
Re: y+ calculations

Re: y+ calculations
hi Thanks for the info,
but I wanted the formula to calculate the Y+ from the flow variables like Re ,etc henry 
Re: y+ calculations
hi
Could some one give the formula please. joe 
Re: y+ calculations
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<y+<5 The intermediate zone : 5<y+<30 The turbulent zone : 30<y+<500 Regards. 
Re: y+ calculations
Have a look at the documentation, it's in there.
Robin 
Re: y+ calculations
hi
Patrice thanks soo much , do you know how the shear velocity is calculated. thanks again joseph 
Re: y+ calculations
Hello, All:
I am very interested in this topic. I am using CFD4 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)? MinHua Wang 
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