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-   -   Boundary condition problem for open channel flow (http://www.cfd-online.com/Forums/cfx/27006-boundary-condition-problem-open-channel-flow.html)

Andy February 9, 2009 08:12

Boundary condition problem for open channel flow
 
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...


niravtm007 April 19, 2012 06:33

apply pressure outlet
 
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 May 6, 2012 04:22

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

niravtm007 May 6, 2012 04:46

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

yoni May 6, 2012 08:08

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?

rsaha September 11, 2012 23:29

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,

oinch October 1, 2012 02:32

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

ghorrocks October 1, 2012 07:33

This is the CFX forum. Best ask questions on Fluent in the Fluent forum.

oinch October 1, 2012 07:45

sorry,

thanks


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