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-   -   [Other] Concept behind Y+ (http://www.cfd-online.com/Forums/ansys-meshing/81030-concept-behind-y.html)

sidspark12 October 14, 2010 03:59

Concept behind Y+
 
hello all,

can anybody explain me the concept behind Y+...........how do we set the value of Y+.....and how we calculate ?

what if the value of Y+ is very large or very less........?

thanx...........

dst October 15, 2010 06:36

Hi sidspark12,

all depends on your turbulence model. Wrong y+ parameters can(!) lead to wrong functioning of turbulence model (but, not so easy, as usual - everything depends on everything).

Let's say that one general approach (but not the rule) for y+ for two-equation models is
y+ ~ 1 for k-w
y+ ~ 30 for k-e

Of course, it is quite difficult to have constant y+ in all the surfaces, but usually you can try to be near to that values.

For y+ information you can check in solver's manuals - like in CFX manual or Fluent manual.

Regards,
DST

sidspark12 October 15, 2010 08:03

Hello DST

thanx...a ....lot...

Right now i am solving the case of FRANCIS TURBINE. for that i am using k-e model......and the value of y+ is around 12........now in my case the value of y+ is not same for every element because of the bldae design. .........now as u said in k-e model the value of y+ is near 30..........so how should i improve the value of y+.......?

after this i will also solve the same case with k-w model........

thanx......


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