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-   -   Velocity in VR Viewer (http://www.cfd-online.com/Forums/phoenics/51307-velocity-vr-viewer.html)

Cheng-Hu Hu December 6, 2001 17:00

Velocity in VR Viewer
 
Hi,

Could anybody tell me how the VR Viewer calculate the velocities? I've noticed that the velocity field resolved by VR viewer is somewhat questionable, i.e. the velocity does not equal to its value of SQRT(u**2+v**2+w**2) in a cell. The VR Viewer can plot x, y, z velocities respectively and the probe can report the values at any point in the domain but the velocities in some points just does not equal to the value that has been mentioned above. The discrepancy is noticeablely large when the probe is placed in the grids near the solid surface. I am using PHOENICS 3.4 for windows NT to simulate the airflow around a couple of buildings.

Cheers,

Cheng-Hu

Bryan Lam December 13, 2001 04:11

Re: Velocity in VR Viewer
 
Dear chenghu:

As what you described in the phoenics forum, i think the reason is the staggered grid. Namely the velocity is really equal to the value of sqrt(u**2+v**2+w**2) in a cell, but when we mention the value of the u, v or w, there should be a move of a half grid. I think that the shown value of the total volocity of cell is the result of consideration of staggered grid by phoenics.

I hope this helps you.

Bryan


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