# Boundary condition problem for open channel flow

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 February 9, 2009, 07:12 Boundary condition problem for open channel flow #1 Andy Guest   Posts: n/a hello, i am trying to make a simulation, i have a long 2D channel. there is an circular bump in the flow path, which affect the flow path and stream line. it is a air-water, two phase flow situation, i want to put boundary condition, such that i will get the jump after the obstruction i.e. flow should convert from super critical flow to sub critical flow, as i change the parameters like water inlet height and velocity. i put an inlet boundary condition is water inlet velocity, but i am confused what to put at outlet boundary condition, because the pressure at water is hydrostatic and at air, it is constant. similar problem is available in tutorial 7 of cfx, but there people make intentionally a downstream pressure by defining downstream height because they want to show only the interface, but how would we know the downstream height until there is flow. i want to see hydraulic jump. please try this. thank you...

 April 19, 2012, 06:33 apply pressure outlet #2 Member   Nirav Join Date: Jul 2011 Posts: 43 Rep Power: 14 apply pressure outlet and select open chanel flow in VOF scheme, the at out let you can define the height of free surface, use anysys help from ansys 13 and search for open channel flow you will get a good idea. yoni likes this.

 May 6, 2012, 04:22 #3 New Member   yoni Join Date: May 2012 Posts: 2 Rep Power: 0 hallo niravtm007 apply pressure outlet and select open chanel flow in VOF scheme,and apply pressure outlet in top of chanel is corect? is open chanel active in top? why the free surface not agree with experimental data in haydraulic jump? what the magnited of the corant number in this case thank you

 May 6, 2012, 04:46 #4 Member   Nirav Join Date: Jul 2011 Posts: 43 Rep Power: 14 hii yoni you can apply courant number of 0.2 , pressure outlet condition at top with out open channel flow ( that is atmospheric pressure at top) and pressure outlet with open channel surface flow at exit by defining bottom surface level and free surface at the exit

 May 6, 2012, 08:08 #5 New Member   yoni Join Date: May 2012 Posts: 2 Rep Power: 0 hii I apply courant number of 0.25 , pressure outlet condition at top with out open channel flow ( that is atmospheric pressure at top) and pressure outlet with open channel surface flow at exit by defining bottom surface level and free surface at the exit whit this condition my result is incorect. how to input atmospheric pressure at top in fluent? where presure refrence in open chanel?

 September 11, 2012, 23:29 #6 New Member     Join Date: Jan 2012 Posts: 8 Rep Power: 14 Hi Yoni, Have you got converged solution using pressure outlet boundary condition at top boundary without activating the open channel boundary condition there? I am also simulating a simple 2D open channel flow. In my case I get converged solution after activating the open channel condition at the top boundary. Which is weird. Thanks,

 October 1, 2012, 02:32 #7 New Member   Join Date: Sep 2012 Posts: 7 Rep Power: 13 Hello everybody, I am new in Fluent and I am trying to do the same simulation. I know that a tutorial for free surface flow over a bump in CFX exists and I am trying to use it to simulate the same thing in Fluent. My question is : it is compulsory to use an UDF for the boundary conditions? My second question is: in design modeler I drew a sketch of a rectangle with a circular bump and I used : create a surface with the sketch, then I used Meshing to mesh . My third question is: do I need to create a surface name for each faces ? Thanks for your help!! Samia

 October 1, 2012, 07:33 #8 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,748 Rep Power: 143 This is the CFX forum. Best ask questions on Fluent in the Fluent forum.

 October 1, 2012, 07:45 #9 New Member   Join Date: Sep 2012 Posts: 7 Rep Power: 13 sorry, thanks

 June 11, 2016, 07:20 cfd fluent open channel flow #10 New Member   amit agrawal Join Date: Jun 2016 Posts: 5 Rep Power: 10 i have a compound channel 2 inlet and one outlet and there is pier at the center of channel pls tell me about boundary condition..i have only both inlet discharge ..