Pressure gradient boundary condition for LES

Far · November 19, 2012, 12:25

http://www.cfd-online.com/Forums/mai...tau-600-a.html

See above post for details.

I am trying to set-up the LES simulation for the square pipe and having issues in defining boundary conditions. Can any body help me in implementing the pressure gradient across the stream-wise periodic boundaries?

ghorrocks · November 19, 2012, 17:58

Why do you need to define a pressure gradient on the periodic boundaries? Usually preiodic boundaries require no manipulation as the values just transfer across. The pressure gradient takes care of itself.

Far · November 19, 2012, 18:02

I am simulating the infinite long pipe. Therefore to save the computational cost, I have defined the inlet and outlet as translational periodic. For this I need to define the pressure gradient which will derive the flow from inlet to outlet.

PS. This is LES of simple square pipe.

ghorrocks · November 19, 2012, 18:13

I see.

The simple application of this is just to use a additional interface model and set a pressure change. This is trivial - I assume you can do this. This will simply increase the pressure by the amount you specify.

For LES you want the vortex features going out the outlet to come back through the inlet still coherent. I think the simple approach will allow this, vorticies will remain just with the pressure increased. This is probably not exactly correct but the degree of difficulty in gettign the exact approach working is likely to be pretty high

November 19, 2012, 12:25	Pressure gradient boundary condition for LES	#1
Far Senior Member Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,558 Blog Entries: 6 Rep Power: 54	http://www.cfd-online.com/Forums/mai...tau-600-a.html See above post for details. I am trying to set-up the LES simulation for the square pipe and having issues in defining boundary conditions. Can any body help me in implementing the pressure gradient across the stream-wise periodic boundaries?

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November 19, 2012, 17:58		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	Why do you need to define a pressure gradient on the periodic boundaries? Usually preiodic boundaries require no manipulation as the values just transfer across. The pressure gradient takes care of itself.

November 19, 2012, 18:02		#3
Far Senior Member Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,558 Blog Entries: 6 Rep Power: 54	I am simulating the infinite long pipe. Therefore to save the computational cost, I have defined the inlet and outlet as translational periodic. For this I need to define the pressure gradient which will derive the flow from inlet to outlet. PS. This is LES of simple square pipe.

November 19, 2012, 18:13		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	I see. The simple application of this is just to use a additional interface model and set a pressure change. This is trivial - I assume you can do this. This will simply increase the pressure by the amount you specify. For LES you want the vortex features going out the outlet to come back through the inlet still coherent. I think the simple approach will allow this, vorticies will remain just with the pressure increased. This is probably not exactly correct but the degree of difficulty in gettign the exact approach working is likely to be pretty high