[Other] Concept behind Y+

sidspark12 · October 14, 2010, 02:59

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, 05:36

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, 07:03

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......

October 14, 2010, 02:59	Concept behind Y+	#1
sidspark12 New Member siddharth jain Join Date: Sep 2009 Posts: 16 Rep Power: 16	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...........

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October 15, 2010, 05:36		#2
dst New Member Join Date: Oct 2010 Location: Germany Posts: 25 Rep Power: 15	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

October 15, 2010, 07:03		#3
sidspark12 New Member siddharth jain Join Date: Sep 2009 Posts: 16 Rep Power: 16	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......