Expression as boundary condition

kasman_meng · June 15, 2010, 15:33

Hello Everybody! I would like to pose a question.

I am trying to implement different boundary along the same wall. e.g. velocity of 0[m/s] for the first 10mm and 5[m/s] for the next 10mm. First of all, is this done by an expression?
If yes, how exactly? is there the possibility to insert a branch equation in the expressions? Couldn't really find something in the help section......
Any ideas welcome. Ty!

Attesz · June 15, 2010, 16:07

Slice your wall surfaces, then mesh it again, and you will get in CFX-pre this surfaces separately (in mesh regions as primitive's or "named" faces). Now you can set them different velocities. Or if you want to create a continous velocity function along a direction?

ghorrocks · June 15, 2010, 19:26

You can split the wall as Attila suggests, but you can also use a CEL expression to do it. You can use the step() function or if/then statements to generate the function, or you can use a 1D interpolation function with distance along the wall as the input variable. All these options are very simple to do.

antonio · June 16, 2010, 09:45

Just to complement the previous answers you can also divide the wall using the Operation Imprint Faces in the extrude feature from the 3D features toolbar. I think it´s always a good practice to use the least number of "blocks" as possible...

Regards and good luck

kasman_meng · June 16, 2010, 10:04

Hello and thank you for your answers! I already tried a user function and it seems to work! Maybe I'll also try antonio's suggestion but I never done something like that again! Thanks anyway!

June 15, 2010, 15:33	Expression as boundary condition	#1
kasman_meng New Member kits youhara Join Date: May 2010 Posts: 14 Rep Power: 16	Hello Everybody! I would like to pose a question. I am trying to implement different boundary along the same wall. e.g. velocity of 0[m/s] for the first 10mm and 5[m/s] for the next 10mm. First of all, is this done by an expression? If yes, how exactly? is there the possibility to insert a branch equation in the expressions? Couldn't really find something in the help section...... Any ideas welcome. Ty!

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June 15, 2010, 16:07		#2
Attesz Senior Member Attesz Join Date: Mar 2009 Location: Munich Posts: 368 Rep Power: 17	Slice your wall surfaces, then mesh it again, and you will get in CFX-pre this surfaces separately (in mesh regions as primitive's or "named" faces). Now you can set them different velocities. Or if you want to create a continous velocity function along a direction?

June 15, 2010, 19:26		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,850 Rep Power: 144	You can split the wall as Attila suggests, but you can also use a CEL expression to do it. You can use the step() function or if/then statements to generate the function, or you can use a 1D interpolation function with distance along the wall as the input variable. All these options are very simple to do.

June 16, 2010, 09:45		#4
antonio Senior Member Join Date: Jan 2010 Posts: 110 Rep Power: 16	Just to complement the previous answers you can also divide the wall using the Operation Imprint Faces in the extrude feature from the 3D features toolbar. I think it´s always a good practice to use the least number of "blocks" as possible... Regards and good luck

June 16, 2010, 10:04		#5
kasman_meng New Member kits youhara Join Date: May 2010 Posts: 14 Rep Power: 16	Hello and thank you for your answers! I already tried a user function and it seems to work! Maybe I'll also try antonio's suggestion but I never done something like that again! Thanks anyway!