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irfan November 16, 2002 01:27

hello, can any body explain me the physical meaning of YPlus and its significant. If it is ythe input parameter for the software then how it should be selected your suggestions are most welcome irfan

Holidays November 18, 2002 03:15

Re: YPlus
This is general CFD material you could read about in fluid mechanics and CFD textbook such as Versteeg and Malalasekera (1995), or Wilcox (1993) fore more advanced srudents. I would add that there should be a theroretical section in the CFX manual to this effect as well.

Basically its choice (re the position of your first grid points) is related to the closure of your turbulence model at the wall and depends upon the type of models your are going to employ (k-E, low-Re k-E or k-Omega to quote just a few). k-E for example uses a wall function (a simplification for the profiles and therefore an economy in terms of nodes needed locally as well) and there should be no encroachment btw the application region for that algebraic function and the N-S eqns (although the scalable wall function will care for this in CFX-5 nowadays). The other two models quoted as examples are integrated to the walls and therefore require a lot of nodes to define the "logarithmic" profile with the modified N-S eqns therefore leading to y+ ~ 0.1 for the low-Re k-E .

y+ is therefore a non-dimensional distance to the wall equal to the product of the shear velocity by the distance to the wall over the cinematic viscosity, the shera velocity being related to the square root of k locally.

irfan November 19, 2002 04:33

Re: YPlus
Thanks for this precious information.


After getting the solution, I am facing a difficulty in judging that the particular set of input turbulence parameters (example; Dissipation length scale & Turbulence intensity in standard K E modal), being selected are correct. For this, should I check the residuals of turbulence only or do I need to check something else. I will appreciate your guidance in this regard


rambol November 20, 2002 10:13

Re: YPlus
y+ ~ 0.1 for the low-Re k-E ?Are you sure?the reference book of cfx requires Y+<1 in low-Re k-E ,I found the mesh would be very fine at that time and the result is not satisfactory.If the y+<0.1,Oh,my god!But if It is necessary,I will do it.

Holidays November 20, 2002 12:00

Re: YPlus
You could check this out in general CFD or turbulence texbooks. In some cases y+ can get as low as 0.1.

rambol November 20, 2002 20:59

Re: YPlus
thank you

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