Turbulent Schmidt Number default value

Forrest_Lei · June 7, 2010, 06:47

Hi all,

Recently I am revisiting some of the cavity natural convection cases I did before using CFX version 12 (previously the work was done by version 5.7 if i remember correctly). If I turn on the buoyancy 'production and dissipation', the turbulent schmidt number is now 2.0 by default, and I know it was 0.9 before. Does anyone know what are the underlying reasons to change this default value? What kind of difference we would expect with these two values for a closed cavity natural convection case? The case I am looking at right now is a well defined case, 2D, vertical walls have a temperature difference, the horizontal walls are adiabatic.

thank you for your comments

Regards,
Forrest

ghorrocks · June 7, 2010, 07:07

I have no idea why the turb schmidt number changed. If you don't like it then change it back! If you go through the release notes of the versions between 5.7 and 12 you should find a reason for the change. Alternately contact CFX support.

And by the way, there are not many turbulent natural convection cases which are 2D. They almost always develop 3D transient flow features if the Rayliegh number is high enough to generate turbulence.

Forrest_Lei · June 7, 2010, 07:29

Dear Glenn,

Thanks for your quick reply. I am not quite sure when this was changed, since versions 10, 11, or 12, I will have a look the release notes if I still could find them for these versions.

I agree with you about the natural convection cases, most of the time they do not behave exactly as expected numerically. There were some experimental investigations in the past, researchers reported 2D characteristics of their 3D experiments, especially in the centre of their test cavity.

Regards,
Forrest

June 7, 2010, 06:47	Turbulent Schmidt Number default value	#1
Forrest_Lei New Member Forrest Join Date: Oct 2009 Posts: 15 Rep Power: 17	Hi all, Recently I am revisiting some of the cavity natural convection cases I did before using CFX version 12 (previously the work was done by version 5.7 if i remember correctly). If I turn on the buoyancy 'production and dissipation', the turbulent schmidt number is now 2.0 by default, and I know it was 0.9 before. Does anyone know what are the underlying reasons to change this default value? What kind of difference we would expect with these two values for a closed cavity natural convection case? The case I am looking at right now is a well defined case, 2D, vertical walls have a temperature difference, the horizontal walls are adiabatic. thank you for your comments Regards, Forrest

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June 7, 2010, 07:07		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	I have no idea why the turb schmidt number changed. If you don't like it then change it back! If you go through the release notes of the versions between 5.7 and 12 you should find a reason for the change. Alternately contact CFX support. And by the way, there are not many turbulent natural convection cases which are 2D. They almost always develop 3D transient flow features if the Rayliegh number is high enough to generate turbulence.

June 7, 2010, 07:29		#3
Forrest_Lei New Member Forrest Join Date: Oct 2009 Posts: 15 Rep Power: 17	Dear Glenn, Thanks for your quick reply. I am not quite sure when this was changed, since versions 10, 11, or 12, I will have a look the release notes if I still could find them for these versions. I agree with you about the natural convection cases, most of the time they do not behave exactly as expected numerically. There were some experimental investigations in the past, researchers reported 2D characteristics of their 3D experiments, especially in the centre of their test cavity. Regards, Forrest