# Define y+ in fluent

Member
in Fluids

Hi every one

I want to plot Y+ vs U+ but the value of y+ is very small because I used y+=0.1 to 1 For LES model so how can I get a y+ values like 100 or 300

I read some of the discussions and some of them talk about define y+ how can I define it???

• Forum Coordinator
edited May 18

Please post the questions in appropriate category. Moving this question to other category to get better response.

Moving to fluid dynamics.

You will need to coarsen the mesh to increase y+ value.

At the same time, for LES it is required to get Y+ as 1.

Regards,

Keyur

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• Member
edited May 18

ok, I will move it. but I need to plot some quantities with y+ so I need to get y+ at least =20

• GermanyForum Coordinator
edited May 18

You need to code the expression for Yplus so that you can plot along a line normal to the wall.

• Member
edited May 18

You need to code the expression for Yplus so that you can plot along a line normal to the wall.

I know that but I don't have any idea about the code and how can i write it, because I'm a beginner user

the wall yplus read only first layer so If you have any information that can help me, I will be grateful

• UKForum Coordinator
edited May 18
• Member
edited May 18

Mr. rwoolhou I don't waste your time I try to put y+=1 but that not enough so I need the code to define y+ and I need more than one mesh, so I want to test the effect of y + on simulation

• Member
edited May 18

I read discussions about finding y+ and Mr. abenhad talk about define y+ from a code because the wall y+ in the fluent don't give enough value of y+

• GermanyForum Coordinator
edited May 18
You define a custom field function with the expression of yplus from manual which you later can plot along any line.
• Member
edited May 18

I try to do that yplus=(y*ut /kinematic viscosity)  but her what y mean wall distance or coordinate y or what

• GermanyForum Coordinator
edited May 18
Wall distance
• Member
edited May 18

thank you very much

• Member
edited May 18

plot y+ vs ut

that what I got it

• GermanyForum Coordinator
edited May 19

Looks good or not? Just remember that Cell Wall Distance is the distance to the next wall.

• Member
edited May 19

the value of y+ is also small so not good I need a big value like 20 or 30

• UKForum Coordinator
edited May 20

Then use a coarser mesh.

• Member
edited May 20

Mr.rwoolhou I know courser mesh gives a large value of y+ but I ask if I can get a large value of y+ from  a fine mesh