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study the act of emtying of a tank(no inlet and an outlet)

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Old   May 11, 2009, 01:05
Question study the act of emtying of a tank(no inlet and an outlet)
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hi every one
i want yo study the vortex made by emtying a tank or a pool whit a hole(outlet) in the bottom of it
but how can i define the gradient of fluid at the surface of it i mean how can i see falling down(lowering ) the fluid surface ?

thanks
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Old   May 11, 2009, 02:26
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Hi,

The free surface will lower as the level goes down and probably form a low point a t the vortex. Is this what you mean? To see this is CFD-Post you draw an iso-surface of volume fraction = 0.5.

Have a look at the flow over a bump tutorial problem to see how to set up a basic free surface flow simulation.

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Old   May 12, 2009, 23:51
Question how to define CEL
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thanks gelen for reply
you got what axaclly i mean.
i see that tutorial but i cant understand that CEL defined for example
DownH
0.022 [m]
?
and
UpH =0.069 ?
and
this exprestion i brought downer.
can you explain a little more what do i need? for that vortex problem
and i should remind that the problem is transient but the tuterial was not
and i didnt see eny volum fraction in water in that problem
can you send me the CEL needed
for the vortex problem whit dimention of a cylender whit 1 mheight filld up with water and the diameter of 0.5 m and a hol in the midel with 0.1m ?
i will realy apratiat that


UpVFAir
step((y-UpH)/1[m])
UpPres
DenH*g*UpVFWater*(UpH-y)
DownVFAir
step((y-DownH)/1[m])
DownVFWater
1-DownVFAir
DownPres
DenH*g*DownVFWater*(DownH-y)
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Old   May 13, 2009, 18:43
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Hi,

Sorry, I don't have time to set up demo problems for you. Ask CFX support for a demo problem or do a CFX training course. Otherwise do as many of the tutorials which come with CFX as you can so you can gain experience in using the software.

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Old   May 14, 2009, 00:28
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tanks anyway
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Old   May 14, 2009, 04:15
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From that tutorial (http://www.kxcad.net/ansys/ANSYS_CFX/help/help/Tutorials/i1315642.html):

"These are expressions for the downstream free surface height, the density of the fluid, ..."
DownH 0.022 [m]
DenH 998 [kg m^-3]
....
....
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Old   November 3, 2009, 06:15
Default DownH= surface height below water free surface?
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Down stream means DownH= surface height below water free surface? and what UpH mean?
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Old   November 3, 2009, 06:34
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http://www.kxcad.net/ansys/ANSYS_CFX.../i1315642.html

"These are expressions for 1) the downstream free surface height, 2) the density of the fluid, 3) the upstream volume fractions of air 4) and water, 5) the upstream pressure distribution, 6) the downstream volume fractions of air 7) and water, and 8) the downstream pressure distribution."

Name Definition
1) DownH: 0.022 [m]
2) DenH: 998 [kg m^-3]
3) UpVFAir: step((y-UpH)/1[m])
4) UpVFWater: 1-UpVFAir
5) UpPres: DenH*g*UpVFWater*(UpH-y)
6) DownVFAir: step((y-DownH)/1[m])
7) DownVFWater: 1-DownVFAir
8) DownPres: DenH*g*DownVFWater*(DownH-y)
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