Question about YPLUS and near wall treatment

Jordi P. · June 26, 2014, 09:01

Good afternoon!

I have a domain within there are a Yplus with values between 25/50. I've found that from an Yplus around 24 I have to use the logarithmic treatment to compute the near wall effects how it shows the Von Karman, "law of the wall". But, is and Yplus 25 too much near of the "limit" of the logarithmic region for using the Standard Wall treatment?. And other question.
When is essential to capture the thermal boundary layer of a wall? and
(third question) If I want to capture it, I have to use the "Enhanced Wall Treatment" with "Thermal Effects" activated?

Thanks in advance!

Jordi (

)

86lolo · June 27, 2014, 19:29

Jordi
As far as I know, you should try to avoud y+ values between 5 and 30. But practically, if you want to solve the flow all the way to the wall, people tend not to use y+ just below 5, but below 1.
About the thermal layer... I guess it is important if the thermal effects of your problem are important. Is it the case?
I can't help about ["Enhanced Wall Treatment" with "Thermal Effects" activated], maybe someone else could help here

Jordi P. · July 3, 2014, 08:22

Hello! Thanks for your response! I've solved the problem taking an Yplus around 50 this way I'm sure that I'm in the logarithmic zone (I dont have big gradients in the domain); I cannot use an Yplus below 1 so this it will imply a very large number of elements in my domain.
About the thermal layer I've to look for some information in relation with how to know the thickness of this layer in some book; good bye!

Blanco · July 3, 2014, 11:47

Hi Jordi,

having an yplus equal to 50 is ok if you don't want to have a detailed description of what is happening inside the wall boundary layer, at least in the part very close to the wall. Usually an y+ between 30 and 100 should be ok if you want to correctly describe the wall layer using the log-equation.
When you want to carefully describe the wall layer, that's when you need an y+ down to 1.
Coming to the thermal wall layer, that is important to be solved if you are simulating a compressible flow with relevant heat flux between wall and fluid, or between different zones inside the fluid. If you are simulating an incompressible flow, simply forget the thermal wall layer, you are not simulating the "physical" temperature at all.

Regards

Jordi P. · July 3, 2014, 12:03

Thanks Andrea, I'll take into account what you told me, my flow is incompresible yes.

Regards!

June 26, 2014, 09:01	Question about YPLUS and near wall treatment	#1
Jordi P. New Member Jian Join Date: Aug 2013 Location: Barcelona (Spain) Posts: 9 Rep Power: 13	Good afternoon! I have a domain within there are a Yplus with values between 25/50. I've found that from an Yplus around 24 I have to use the logarithmic treatment to compute the near wall effects how it shows the Von Karman, "law of the wall". But, is and Yplus 25 too much near of the "limit" of the logarithmic region for using the Standard Wall treatment?. And other question. When is essential to capture the thermal boundary layer of a wall? and (third question) If I want to capture it, I have to use the "Enhanced Wall Treatment" with "Thermal Effects" activated? Thanks in advance! Jordi ()

June 27, 2014, 19:29		#2
86lolo New Member Manuel Join Date: Jan 2014 Posts: 18 Rep Power: 12	Jordi As far as I know, you should try to avoud y+ values between 5 and 30. But practically, if you want to solve the flow all the way to the wall, people tend not to use y+ just below 5, but below 1. About the thermal layer... I guess it is important if the thermal effects of your problem are important. Is it the case? I can't help about ["Enhanced Wall Treatment" with "Thermal Effects" activated], maybe someone else could help here

July 3, 2014, 08:22		#3
Jordi P. New Member Jian Join Date: Aug 2013 Location: Barcelona (Spain) Posts: 9 Rep Power: 13	Hello! Thanks for your response! I've solved the problem taking an Yplus around 50 this way I'm sure that I'm in the logarithmic zone (I dont have big gradients in the domain); I cannot use an Yplus below 1 so this it will imply a very large number of elements in my domain. About the thermal layer I've to look for some information in relation with how to know the thickness of this layer in some book; good bye!

July 3, 2014, 11:47		#4
Blanco Senior Member Blanco Join Date: Mar 2009 Location: Torino, Italy Posts: 193 Rep Power: 17	Hi Jordi, having an yplus equal to 50 is ok if you don't want to have a detailed description of what is happening inside the wall boundary layer, at least in the part very close to the wall. Usually an y+ between 30 and 100 should be ok if you want to correctly describe the wall layer using the log-equation. When you want to carefully describe the wall layer, that's when you need an y+ down to 1. Coming to the thermal wall layer, that is important to be solved if you are simulating a compressible flow with relevant heat flux between wall and fluid, or between different zones inside the fluid. If you are simulating an incompressible flow, simply forget the thermal wall layer, you are not simulating the "physical" temperature at all. Regards

July 3, 2014, 12:03		#5
Jordi P. New Member Jian Join Date: Aug 2013 Location: Barcelona (Spain) Posts: 9 Rep Power: 13	Thanks Andrea, I'll take into account what you told me, my flow is incompresible yes. Regards!