Automatic wall function parameters

MoritzP · April 6, 2016, 08:55

Hi,
i've got a question concerning the parameters used in the automatic wall function treatment when using the SST model. I am simulating the case of a temperatur dependent viscosity oil in a 2D-channel with wall heating. As shown in some papers with DNS in this topic, the elevation of the log-layer in the velocity distribution ist highly influenced by the viscosity ratio near the wall due to the heating.
I have already simulated my case with a fine mesh and got the same result for the velocity distribution and the wall shear. Now the aim of that study is to get an acceptable result for a coarse mesh by implementing a model change. Therefore I want to modify the parameter C in the log law used for $u_{\tau}$ : $u_{\tau}=\frac{u}{\frac{1}{\kappa}ln(y^{*})+C}$
I could not find anything on this case in the manual or other forum threads until now. Thanks for your help in advance

ghorrocks · April 6, 2016, 19:14

Quoting Opaque:

Quote:

After selecting the RNG model, open the Advanced Controls for the turbulence model setup, and overwrite the Eddy Viscosity value by your own CEL expression.

This is in reference to the RNG model but the same thing applies to all eddy viscosity models.

From this thread: http://www.cfd-online.com/Forums/cfx...nce-model.html

MoritzP · April 7, 2016, 10:39

Thanks for your reply Glenn

I wasn't referring to the eddy viscosity but to the wall friction velocity.
Anyway I found a way to modify the wall function for the momentum by activating beta features for physics and implementing a user defined wall function coefficient.

ghorrocks · April 7, 2016, 18:15

Oops, sorry - looks like I did not read your post close enough. Good to hear you found a way anyway.

By the way, you could probably also do this by defining your wall with a specified wall shear stress.

April 6, 2016, 08:55	Automatic wall function parameters	#1
MoritzP New Member Moritz Join Date: Apr 2016 Posts: 2 Rep Power: 0	Hi, i've got a question concerning the parameters used in the automatic wall function treatment when using the SST model. I am simulating the case of a temperatur dependent viscosity oil in a 2D-channel with wall heating. As shown in some papers with DNS in this topic, the elevation of the log-layer in the velocity distribution ist highly influenced by the viscosity ratio near the wall due to the heating. I have already simulated my case with a fine mesh and got the same result for the velocity distribution and the wall shear. Now the aim of that study is to get an acceptable result for a coarse mesh by implementing a model change. Therefore I want to modify the parameter C in the log law used for $u_{\tau}$ : $u_{\tau}=\frac{u}{\frac{1}{\kappa}ln(y^{*})+C}$ I could not find anything on this case in the manual or other forum threads until now. Thanks for your help in advance

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April 7, 2016, 10:39		#3
MoritzP New Member Moritz Join Date: Apr 2016 Posts: 2 Rep Power: 0	Thanks for your reply Glenn I wasn't referring to the eddy viscosity but to the wall friction velocity. Anyway I found a way to modify the wall function for the momentum by activating beta features for physics and implementing a user defined wall function coefficient.

April 7, 2016, 18:15		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Oops, sorry - looks like I did not read your post close enough. Good to hear you found a way anyway. By the way, you could probably also do this by defining your wall with a specified wall shear stress.