how can i get the velocity values

shine · March 9, 2010, 21:54

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)

Linh.Hoang · March 10, 2010, 03:39

Hello shine,
it´s 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 it´s computed: vabs= sqrt(U1**2+V1**2+W1**2)!!
Hope this helps
Linh

Koolifant · March 10, 2010, 03:43

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).

Koolifant · March 10, 2010, 03:45

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.

shine · March 10, 2010, 05:11

Quote:

Originally Posted by Linh.Hoang

Hello shine,
it´s 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 it´s computed: vabs= sqrt(U1**2+V1**2+W1**2)!!
Hope this helps
Linh

dear Linh.Hoang
thanks~
u did help me a lot!!!!

shine · March 10, 2010, 05:13

dear Koolifant

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

March 9, 2010, 21:54	how can i get the velocity values	#1
shine New Member Shine.Hsu Join Date: Mar 2010 Location: Taiwan, Taipei Posts: 3 Rep Power: 16	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(u2+v2+w*2) Last edited by shine; March 9, 2010 at 22:20.*

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March 10, 2010, 03:39		#2
Linh.Hoang New Member Join Date: May 2009 Location: Germany Posts: 25 Rep Power: 16	Hello shine, it´s 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 it´s computed: vabs= sqrt(U12+V12+W1**2)!! Hope this helps Linh

March 10, 2010, 03:43		#3
Koolifant New Member Join Date: Mar 2009 Posts: 15 Rep Power: 17	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(u2+v2+w**2)... If you don't have cartesian coords, check if IURPRN perhaps is set to a non-zero value (zero is default).

March 10, 2010, 03:45		#4
Koolifant New Member Join Date: Mar 2009 Posts: 15 Rep Power: 17	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.

March 10, 2010, 05:13		#6
shine New Member Shine.Hsu Join Date: Mar 2010 Location: Taiwan, Taipei Posts: 3 Rep Power: 16	dear Koolifant thank u~~~~~ appreciated ur help!!!!