boundary condition

az_f · October 1, 2009, 20:18

Hi All
I have bifurcation model including two branches with different sizes. So I can not estimate the pressure or velocity at these two and assuming pressure zero is not correct. I was wondering can we add some subroutine to define boundary condition at outlet. In that case how can I do that?

Many Thanks

ghorrocks · October 2, 2009, 01:09

Well, you have to know something about it! It is pointless even thinking about CFD until you have a set of boundary conditions which properly specify the flow. You need to have a think about how this flow is defined and where your boundaries should go.

If you don't know either velocity or pressure then it is not a good place to put a boundary. You should move the boundary to somewhere where some conditions are known.

az_f · October 2, 2009, 01:14

Hi Glenn,
I mean physiologically we couldn't measure the velocity and pressure at outlet. Therefore we have to calculate the flow pressure or velocity according to the diameter of the branches. My question is how I can assign this boundary in cfx -pre as an additional variable or I don't know....

ghorrocks · October 5, 2009, 18:41

Do you know the velocity or pressure? Is it a function of something? You can set the velocity of a velocity boundary or the pressure of a pressure boundary to be an expression so you can link it to other flow features if you like.

October 1, 2009, 20:18	boundary condition	#1
az_f Member Join Date: Mar 2009 Posts: 48 Rep Power: 17	Hi All I have bifurcation model including two branches with different sizes. So I can not estimate the pressure or velocity at these two and assuming pressure zero is not correct. I was wondering can we add some subroutine to define boundary condition at outlet. In that case how can I do that? Many Thanks

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October 2, 2009, 01:09		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	Well, you have to know something about it! It is pointless even thinking about CFD until you have a set of boundary conditions which properly specify the flow. You need to have a think about how this flow is defined and where your boundaries should go. If you don't know either velocity or pressure then it is not a good place to put a boundary. You should move the boundary to somewhere where some conditions are known.

October 2, 2009, 01:14		#3
az_f Member Join Date: Mar 2009 Posts: 48 Rep Power: 17	Hi Glenn, I mean physiologically we couldn't measure the velocity and pressure at outlet. Therefore we have to calculate the flow pressure or velocity according to the diameter of the branches. My question is how I can assign this boundary in cfx -pre as an additional variable or I don't know....

October 5, 2009, 18:41		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	Do you know the velocity or pressure? Is it a function of something? You can set the velocity of a velocity boundary or the pressure of a pressure boundary to be an expression so you can link it to other flow features if you like.