unit of U in paraviewer?

A subforum specific to the development of the OpenFoam-based workbenches ( Cfd https://github.com/qingfengxia/Cfd and CfdOF https://github.com/jaheyns/CfdOF )

Moderator: oliveroxtoby

Post Reply
tjboon
Posts: 5
Joined: Wed Jun 22, 2022 1:02 pm

unit of U in paraviewer?

Post by tjboon »

Hi guys, I get crazy high values in my simulation to the power of 14 while the outlet speed set is only 5m/s? so my question is if im doing anything wrong or whats the unit of U
thschrader
Veteran
Posts: 3129
Joined: Sat May 20, 2017 12:06 pm
Location: Germany

Re: unit of U in paraviewer?

Post by thschrader »

openFOAM uses SI units.
See U/p files after case writing.
EDIT:
the results shown in paraview correspond to openFOAM.
https://www.cfdsupport.com/openfoam-tra ... ode51.html
https://doc.cfd.direct/openfoam/user-gu ... ile-format
dimensions.JPG
dimensions.JPG (28.11 KiB) Viewed 2499 times
tjboon
Posts: 5
Joined: Wed Jun 22, 2022 1:02 pm

Re: unit of U in paraviewer?

Post by tjboon »

thschrader wrote: Wed Jul 06, 2022 4:28 pm openFOAM uses SI units.
See U/p files after case writing.
EDIT:
the results shown in paraview correspond to openFOAM.
https://www.cfdsupport.com/openfoam-tra ... ode51.html
https://doc.cfd.direct/openfoam/user-gu ... ile-format
dimensions.JPG
So the U in paraviewer is actually dynamic viscosity and not velocity?
User avatar
r.tec
Posts: 533
Joined: Thu Oct 23, 2014 4:06 pm
Location: Bad Münstereifel, NRW, Germany
Contact:

Re: unit of U in paraviewer?

Post by r.tec »

No, U ist velocity with the dimension [m/s]
tjboon
Posts: 5
Joined: Wed Jun 22, 2022 1:02 pm

Re: unit of U in paraviewer?

Post by tjboon »

r.tec wrote: Wed Jul 13, 2022 8:57 am No, U ist velocity with the dimension [m/s]
Is there anyway how I can see that in my model? What actually is the velocity in m/s?
User avatar
r.tec
Posts: 533
Joined: Thu Oct 23, 2014 4:06 pm
Location: Bad Münstereifel, NRW, Germany
Contact:

Re: unit of U in paraviewer?

Post by r.tec »

Yes, in Paraview you can chose "U", then the approriate colour corresponds to velocity U. And as Thomas wrote OpenFOAM takes SI-units, in this case [meter per second or m/s]. Or you can filter for Glyph in Paraview to show the velocity-vectors. But you must play a bit around to find the best relation of Glyph-size to velocity.
User avatar
r.tec
Posts: 533
Joined: Thu Oct 23, 2014 4:06 pm
Location: Bad Münstereifel, NRW, Germany
Contact:

Re: unit of U in paraviewer?

Post by r.tec »

Example 2D CFD:
2022-02-07 Animated.gif
2022-02-07 Animated.gif (902.62 KiB) Viewed 2310 times
This animated .gif shows what I mean. The fine lines are streamlines, the colour shows the velocity, or more precise the changes of velocity.

But I do not know what the flash-like artefacts are and where they come from. Not nice but no influence on the results.
trijonb
Posts: 10
Joined: Mon May 24, 2021 1:07 am

Re: unit of U in paraviewer?

Post by trijonb »

r.tec wrote: Wed Jul 13, 2022 4:15 pm But I do not know what the flash-like artefacts are and where they come from. Not nice but no influence on the results.
These look like processor patches (ie results processed on a decomposed mesh). Looks like you may have used np=4?
KAKM
Posts: 109
Joined: Tue May 04, 2021 12:17 am

Re: unit of U in paraviewer?

Post by KAKM »

tjboon wrote: Wed Jul 06, 2022 10:49 am I get crazy high values in my simulation to the power of 14 while the outlet speed set is only 5m/s
Even if your simulation had somehow gotten set to nm/s (unlikely), you would still only be seeing 10^9 or so. Sounds like your simulation diverged/blew up. Did you use a velocity inlet? You can get weird results if there's nothing to bound the pressure. Or you might have used too large of a timestep, or had bad mesh elements somewhere. It's hard to say without more information on your simulation.
Post Reply