Spalart-Allmaras y+

Mr.Pinka · June 3, 2014, 21:39

Hi!

I am running an aircraft simulaction in Fluent Ansys 15 in cruise condition (M=0.8, h=11km...).

I am using a SA model and I have read that the y+ value must be y+=~1 or 30<y+<150 but I am a little bit confused about it. Is it correct? And why is there this difference between the two ranges?

Thank you very much!

Bionico · June 4, 2014, 04:34

Hello Mr. Pinka,
if you choose a k-epsilon turbulence model, you can define the Near Wall Treatment: it depends on your Y+ (Enhanced Wall Function for Y+=1 and Standard Wall Function for Y+>30).
Spalart-Allmaras doesn't let you to change the Near Wall Treatment, so I suggest reading Fluent Manual: probably this turbulence model can switch automatically from a function to another according to Y+ (as Scalable Wall Function).

Kind Regards

Mr.Pinka · June 4, 2014, 05:42

Thank You Bionico,

Yes, I have been reading the Fluent Manual and I have found that the Y+ Value must be Y+~1 or Y+>30 for Sparlat-Allmaras model.

I suppose that the model use a wall funtion for Y+>30.

If somebody disagrees please tell why.

Thank You!

Regards!

ghost82 · June 4, 2014, 07:23

Yes Karla, from fluent manual:

In summary, for best results with the Spalart-Allmaras model, you should use either a very fine near-wall mesh spacing (on the order of

) or a mesh spacing such that

.

Mr.Pinka · June 4, 2014, 07:26

Exactly Ghost82,

Thank You very much for the reply.

Regards

June 3, 2014, 21:39	Spalart-Allmaras y+	#1
Mr.Pinka New Member Karla Join Date: Apr 2014 Posts: 5 Rep Power: 12	Hi! I am running an aircraft simulaction in Fluent Ansys 15 in cruise condition (M=0.8, h=11km...). I am using a SA model and I have read that the y+ value must be y+=~1 or 30<y+<150 but I am a little bit confused about it. Is it correct? And why is there this difference between the two ranges? Thank you very much!

June 4, 2014, 04:34		#2
Bionico Senior Member Flavio Join Date: Sep 2011 Location: Brescia, Italy Posts: 181 Rep Power: 15	Hello Mr. Pinka, if you choose a k-epsilon turbulence model, you can define the Near Wall Treatment: it depends on your Y+ (Enhanced Wall Function for Y+=1 and Standard Wall Function for Y+>30). Spalart-Allmaras doesn't let you to change the Near Wall Treatment, so I suggest reading Fluent Manual: probably this turbulence model can switch automatically from a function to another according to Y+ (as Scalable Wall Function). Kind Regards __________________ Bionico

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June 4, 2014, 05:42		#3
Mr.Pinka New Member Karla Join Date: Apr 2014 Posts: 5 Rep Power: 12	Thank You Bionico, Yes, I have been reading the Fluent Manual and I have found that the Y+ Value must be Y+~1 or Y+>30 for Sparlat-Allmaras model. I suppose that the model use a wall funtion for Y+>30. If somebody disagrees please tell why. Thank You! Regards!

June 4, 2014, 07:23		#4
ghost82 Senior Member Rick Join Date: Oct 2010 Posts: 1,016 Rep Power: 26	Yes Karla, from fluent manual: In summary, for best results with the Spalart-Allmaras model, you should use either a very fine near-wall mesh spacing (on the order of ) or a mesh spacing such that .

June 4, 2014, 07:26		#5
Mr.Pinka New Member Karla Join Date: Apr 2014 Posts: 5 Rep Power: 12	Exactly Ghost82, Thank You very much for the reply. Regards