# Which Pressure BC Compatible with Advective Velocity BC?

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 March 2, 2018, 07:09 Which Pressure BC Compatible with Advective Velocity BC? #1 Senior Member   Canakkale Dardanelspor Join Date: Aug 2012 Posts: 135 Rep Power: 14 Hi, I use advective boundary condition for velocity outlet in an incompressible large eddy simulation. I confused myself for which type of boundary condition I must use to ensure outflow pressure condition is compatible with the advective velocity condition? Currently, the pressure condition is fixedValue. Kind regards PS: A similar question seems to be asked here.

March 4, 2018, 05:00
#2
Senior Member

Ehsan Asgari
Join Date: Apr 2010
Posts: 473
Rep Power: 18
Quote:
 Originally Posted by HakikiCanakkaleli Hi, I use advective boundary condition for velocity outlet in an incompressible large eddy simulation. I confused myself for which type of boundary condition I must use to ensure outflow pressure condition is compatible with the advective velocity condition? Currently, the pressure condition is fixedValue. Kind regards PS: A similar question seems to be asked here.
Hi,

I use the same combinaion and I think it's typical.

Regards,
Syavash

 March 4, 2018, 06:43 #3 Senior Member   Canakkale Dardanelspor Join Date: Aug 2012 Posts: 135 Rep Power: 14 Hi, I think this pairing can numerically be viable; however, in physical sense, seems incorrect to me. Because, for a spatiotemporally variant velocity field at the outlet, we force gauge pressure to zero, which shouldn't be the case as we let the velocity field out as is by using advective BC. I would prefer to use zeroGradient pressure, yet this is not possible for incompressible applications. Thanks for your reply,

March 4, 2018, 07:01
#4
Senior Member

Ehsan Asgari
Join Date: Apr 2010
Posts: 473
Rep Power: 18
Quote:
 Originally Posted by HakikiCanakkaleli Hi, I think this pairing can numerically be viable; however, in physical sense, seems incorrect to me. Because, for a spatiotemporally variant velocity field at the outlet, we force gauge pressure to zero, which shouldn't be the case as we let the velocity field out as is by using advective BC. I would prefer to use zeroGradient pressure, yet this is not possible for incompressible applications. Thanks for your reply,
You're welcome. I see your point and I suppose it is true either in case of zeroGradient for velocity at the outlet (instead of advective). However, I have seen a case of boundary-layer simulation which has used zeroGradient for pressure at the outlet. I can provide the link if you wish, but I remember the top boundary was specified as fixedValue for pressure which seems correct to me.

Regards,
Syavash

 March 4, 2018, 08:21 #5 Senior Member   Canakkale Dardanelspor Join Date: Aug 2012 Posts: 135 Rep Power: 14 I would be glad if you could provide me the link, if possible. Kind regards,

March 4, 2018, 08:35
#6
Senior Member

Ehsan Asgari
Join Date: Apr 2010
Posts: 473
Rep Power: 18
Quote:
 Originally Posted by HakikiCanakkaleli I would be glad if you could provide me the link, if possible. Kind regards,

Regards,
Syavash

 November 20, 2019, 23:01 #7 Senior Member   Jianrui Zeng Join Date: May 2018 Location: China Posts: 157 Rep Power: 8 I am also using advective BC for velocity and fixedValue for pressure, is it the correct group of settings? I have found that there is an increase in velocity around the outlet, but I have no idea about it.

 Tags advective bc, large eddy simulation