Air inlet boundary condition for free surface in open channels

mohammad.ramezani · February 15, 2017, 06:21

hi
I want to know that for the Air inlet boundary condition, above the water surface, which of the followings must be determine?
1. A velocity similar to the water velocity?
2. The real air velocity above the water surface?
3. A portion of the water velocity at water inlet?(for example 1/100)
4. A linear velocity profile that at water surface has a velocity equal with water and reaches to zero at higher levels?
5. Or there is no need to define an air inlet, and choosing homogeneous model is sufficient for simulation?
Thanks a lot

ghorrocks · February 15, 2017, 17:58

Please post an image of what you are trying to do showing the flows you want to model and the boundary conditions you intend to use.

mohammad.ramezani · February 17, 2017, 09:11

this is a siphon spillway,in which, in the upstream the reservoir level rises by increasing the discharge.
at the upstream:
1)water inlet height= 0<h<0.35m
2)a wall=0.35<h<0.39
3)air inlet height=0.39<h<0.45m
(water height of the reservoir would not increase than 0.39m)
the down stream is 0.25m drown and the outlet is opening
Thanks a lot for your reply

ghorrocks · February 19, 2017, 18:54

Your questions are in the reverse order to what you should consider them.

First: Homogenoeus or inhomogeneous is chosen depending on whether the free surface is distinct and clear or whether bubbles, foam or other features you do not intend to directly model are present.

Once you have made that choice you need to look at the boundary conditions.

February 15, 2017, 06:21	Air inlet boundary condition for free surface in open channels	#1
mohammad.ramezani New Member mohammad.ramezani Join Date: Dec 2015 Posts: 12 Rep Power: 10	hi I want to know that for the Air inlet boundary condition, above the water surface, which of the followings must be determine? 1. A velocity similar to the water velocity? 2. The real air velocity above the water surface? 3. A portion of the water velocity at water inlet?(for example 1/100) 4. A linear velocity profile that at water surface has a velocity equal with water and reaches to zero at higher levels? 5. Or there is no need to define an air inlet, and choosing homogeneous model is sufficient for simulation? Thanks a lot

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February 15, 2017, 17:58		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	Please post an image of what you are trying to do showing the flows you want to model and the boundary conditions you intend to use.

February 19, 2017, 18:54		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	Your questions are in the reverse order to what you should consider them. First: Homogenoeus or inhomogeneous is chosen depending on whether the free surface is distinct and clear or whether bubbles, foam or other features you do not intend to directly model are present. Once you have made that choice you need to look at the boundary conditions.