What exactly is y+ /yplus and how to calculate it?

Marabelle · September 5, 2013, 07:49

Hello!
I am modeling a transient Heat-transerfer model with the k-kl-w method in FLUENT. I am quite a beginner and still try to understand the whole process. I heard/read lots of people talking about y+ and as I understood in my case I need an y+ around 1 to reach convergence. Did I understand it right that it has something to do with the near-wall grid resolution and the velocity at that place? But I have no idea how to calculate it or how to access it in ANSYS. And then, also how to change this value? Could anyone please help me?
I would really appreciate your answers,
thanks in adveance!
Mara

flotus1 · September 5, 2013, 09:41

The wiki has an article about Yplus:

http://www.cfd-online.com/Wiki/Dimen...e_%28y_plus%29

As you will notice, this dimensionless wall distance depends on the distance from the wall. In simulations of turbulent flows, the Yplus-values are obtained from the width of the first cell near the wall.
Accordingly, if you want to change Yplus for a simulation, you have to change your mesh.

Marabelle · September 5, 2013, 17:14

Thanks for your very quick anwer! The post already cleared it a bit! But still I have to learn a lot more to understand fully, what I am doing when Simulating... respectively what to do to get good convergence...

September 5, 2013, 07:49	What exactly is y+ /yplus and how to calculate it?	#1
Marabelle New Member Tamara Annabelle Join Date: Jul 2013 Posts: 26 Rep Power: 12	Hello! I am modeling a transient Heat-transerfer model with the k-kl-w method in FLUENT. I am quite a beginner and still try to understand the whole process. I heard/read lots of people talking about y+ and as I understood in my case I need an y+ around 1 to reach convergence. Did I understand it right that it has something to do with the near-wall grid resolution and the velocity at that place? But I have no idea how to calculate it or how to access it in ANSYS. And then, also how to change this value? Could anyone please help me? I would really appreciate your answers, thanks in adveance! Mara

September 5, 2013, 09:41		#2
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,399 Rep Power: 46	The wiki has an article about Yplus: http://www.cfd-online.com/Wiki/Dimen...e_%28y_plus%29 As you will notice, this dimensionless wall distance depends on the distance from the wall. In simulations of turbulent flows, the Yplus-values are obtained from the width of the first cell near the wall. Accordingly, if you want to change Yplus for a simulation, you have to change your mesh.

September 5, 2013, 17:14		#3
Marabelle New Member Tamara Annabelle Join Date: Jul 2013 Posts: 26 Rep Power: 12	Thanks for your very quick anwer! The post already cleared it a bit! But still I have to learn a lot more to understand fully, what I am doing when Simulating... respectively what to do to get good convergence...