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how can i get the velocity values

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Old   March 9, 2010, 21:54
Default how can i get the velocity values
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Shine.Hsu
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form PHI file,
i can get U,V,W values
BUT except Velocity

i know i still can get the velocity value via VR-viewer
but i need lots data
i dont wanna record velocities one by one

is there any good way??
plz, help me!!!!!!!

btw,
i found that the velocity value doesnt eaqul to its value of SQRT(u**2+v**2+w**2)

Last edited by shine; March 9, 2010 at 22:20.
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Old   March 10, 2010, 03:39
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Hello shine,
itīs quite easy, when you use the vr editor, then go to output and derived variables setting, there you can set vabs to yes. then you should get the absolute velocity and itīs computed: vabs= sqrt(U1**2+V1**2+W1**2)!!
Hope this helps
Linh
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Old   March 10, 2010, 03:43
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According to Polish:
The velocity variables for which PHOENICS solves are always the resolutes of the velocity vector in the direction of the line joining the grid points on either side of the cell faces at which velocities are stored.
For cartesian grids, these variables are therefore the cartesian velocity resolutes. For cylindrical-polar grids they are the axial, radial and circumferential resolutes. For general curvilinear grids they are the resolutes of the velocity vector in the local direction of the lines connecting the nodal points PE, PN and PH. In vector terminology, U, V and W are equal to the scalar products of the velocity vector with the unit vector aligned with the direction PE, PN and PH respectively.

So VELOCITY should be SQRT(u**2+v**2+w**2)... If you don't have cartesian coords, check if IURPRN perhaps is set to a non-zero value (zero is default).
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Old   March 10, 2010, 03:45
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Sorry shine, i was wrong: the velocity is stored on the cell faces so it still needs averaging over the different faces, which indeed Vabs does account for.
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Old   March 10, 2010, 05:11
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Quote:
Originally Posted by Linh.Hoang View Post
Hello shine,
itīs quite easy, when you use the vr editor, then go to output and derived variables setting, there you can set vabs to yes. then you should get the absolute velocity and itīs computed: vabs= sqrt(U1**2+V1**2+W1**2)!!
Hope this helps
Linh
dear Linh.Hoang
thanks~
u did help me a lot!!!!
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Old   March 10, 2010, 05:13
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dear Koolifant

thank u~~~~~
appreciated ur help!!!!
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