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flow depth in 2D open channel ?

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Old   November 20, 2007, 13:18
Default flow depth in 2D open channel ?
  #1
rodi
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Hi ! I am working in a 2D open channel with VOF,two phase:air /water.The flow depth at the inlet is specialed ,and I get the free surface ,but how to compute the flow depth at outlet? Just multiply Area by volume fraction of water?

Thanks! rodi
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Old   November 20, 2007, 13:56
Default Re: flow depth in 2D open channel ?
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bohis
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Hi, you donīt need to set the depth of water at a outlet. You should only patch the domain according to the physics and adjust the correct backflow at the outlet.

Enjoy your calculation

bye, Jan
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Old   November 21, 2007, 04:42
Default Re: flow depth in 2D open channel ?
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rodi
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Thank you! Maybe i can express my question much clearly~

When the caculation has done,and i got the free surface.During the postprocessing,I want to know the water level at the outlet,what can i do? For 2D simulation,the channel is rectangle. Can i just multiple the water phase fraction by the area of outlet?

Thanks! rodi

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Old   November 21, 2007, 12:34
Default Re: flow depth in 2D open channel ?
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k.baker
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dear rodi you can find the height of water at the outlet from the value of vof at outlet directly by trial and error from the following relation: RL=(1/pi)*(pi-acos(2*(hL/d)-1)+(2*(hL/d)*SQRT(1-(2*(hL/d)^2))

where RL is the vof of liquid (water) & hL is liquid height

I hope this fullfill your request another thing I sent you two emails envolve some questions about your case file which you sent me did you see it or no? did you see my case & data file too? hope to see your reply soon

cheers kb
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Old   November 22, 2007, 01:04
Default Re: flow depth in 2D open channel ?
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sushii
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What is Backflow....and how dose it affects the calculations...? Sometimes when simulating I set backflow volume fraction and backflow turbulent KE....to zero...does it affect the solution...? if yes then how to calculate right backflow volume fraction and turbulent KE...?

---Sushii..
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Old   December 2, 2010, 01:02
Default Open Channel Flow boundary conditions
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Quote:
Originally Posted by rodi
;146875
Thank you! Maybe i can express my question much clearly~

When the caculation has done,and i got the free surface.During the postprocessing,I want to know the water level at the outlet,what can i do? For 2D simulation,the channel is rectangle. Can i just multiple the water phase fraction by the area of outlet?

Thanks! rodi
HI,
I am Rahul. I am also working on Open Channel Flow in Fluent solver. I used
Mass Flow Inlet bc
mass flow of air is 7985.6 kg/s, free surface of water is at 2m, bottom at 0m,
Pressure Outlet bc


In my case the, the channel is rectangular of cross section 4mx3m. Out of 3m height upto 2m there is water. Now I really dont understand what boundary condition should I use for remaining 1m. The geometry is attached herewith.

One more thing to be discussed is that, should I patched volume fraction of water( secondary phase) initially through out the domain. I am trying for steady state simulation.

If somebody have a test case for open channel flow pls do send me on praghanmor@gmail.com

Hoping for ur fruitful suggestions.
Thanks.
Attached Images
File Type: jpg nomenclature_geometry.jpg (21.7 KB, 13 views)
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Old   January 25, 2011, 11:03
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Hi rahulrp
what does your mesh look like?
darp
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Old   January 26, 2011, 00:03
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vig
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Hi,

I you take mass flow inlet boundary for open channel, then both water and air can enter from the same.

Specify free surface level
Specify bottom level
Specify mass flow rate of water as = rho_water *Area_water*Velocity
Specify mass flow rate of air as = rho_air* Area_Air * Velocity

You can use the same velocity for both water and air.
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