Computational Fluid Dynamics (CFD) workbench using OpenFOAM

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

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Crossleyuk
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Re: Computational Fluid Dynamics (CFD) workbench using OpenFOAM

Postby Crossleyuk » Tue Apr 16, 2019 6:51 pm

Hi Again,

Lessons moving on great now and greater understanding generation questions starting to be required. I have a static/atmospheric pressure interpretation problem following some forum searches.

I'm setting an inlet pressure of 0Pa and an exit pressure of -1500Pa, i.e. a negative depression relative to atmospheric. FreeCAD and Paraview don't seem to be interpreting this in the way I expected. I am not obtaining my stated negative exit pressure relative to atmospheric.

Is there a "standard" pressure set by FreeCAD? is my -1500Pa being taken as less than a standard pressure rather than negative to atmospheric pressure?

Many thanks in anticipation again.

Michael.
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Re: Computational Fluid Dynamics (CFD) workbench using OpenFOAM

Postby oliveroxtoby » Tue Apr 16, 2019 7:59 pm

Crossleyuk wrote:
Tue Apr 16, 2019 6:51 pm
Hi Again,

Lessons moving on great now and greater understanding generation questions starting to be required. I have a static/atmospheric pressure interpretation problem following some forum searches.

I'm setting an inlet pressure of 0Pa and an exit pressure of -1500Pa, i.e. a negative depression relative to atmospheric. FreeCAD and Paraview don't seem to be interpreting this in the way I expected. I am not obtaining my stated negative exit pressure relative to atmospheric.

Is there a "standard" pressure set by FreeCAD? is my -1500Pa being taken as less than a standard pressure rather than negative to atmospheric pressure?

Many thanks in anticipation again.

Michael.
For incompressible flow, the pressure used by OpenFOAM and shown in Paraview is actually a 'kinematic pressure', p/rho. Could this be the source of the discrepancy?
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Crossleyuk
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Re: Computational Fluid Dynamics (CFD) workbench using OpenFOAM

Postby Crossleyuk » Tue Apr 16, 2019 8:19 pm

Thanks Oliver,

I see that will clarify the magnitude of the reported value so it's very valuable, but not it's value relative to atmospheric pressure. If I have the outlet connected to the inlet of a fan it should be approaching a depression, below atmospheric pressure (1500Pa gauge). I need to obtain a static pressure drop between inlet and outlet with no reference to any dynamic pressure terms. What I'm looking to obtain is the average static gauge pressure over the entire face of the outlet (exit). Thanks though, I actually have a further flow section to add to the model, so I'll take another look in the morning and apply your suggestion.

Cheers

Michael
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Re: Computational Fluid Dynamics (CFD) workbench using OpenFOAM

Postby thschrader » Tue Apr 16, 2019 9:11 pm

Crossleyuk wrote:
Tue Apr 16, 2019 8:19 pm
Thanks Oliver,

I see that will clarify the magnitude of the reported value so it's very valuable, but not it's value relative to atmospheric pressure. If I have the outlet connected to the inlet of a fan it should be approaching a depression, below atmospheric pressure (1500Pa gauge). I need to obtain a static pressure drop between inlet and outlet with no reference to any dynamic pressure terms. What I'm looking to obtain is the average static gauge pressure over the entire face of the outlet (exit). Thanks though, I actually have a further flow section to add to the model, so I'll take another look in the morning and apply your suggestion.

Cheers

Michael
Can you post a model? Please in detail. What do you want to calculate?
How about a FC-file with your cfd-wb parameters..
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Re: Computational Fluid Dynamics (CFD) workbench using OpenFOAM

Postby Crossleyuk » Tue Apr 16, 2019 9:18 pm

Thanks again Oliver, I'll look into that in the morning and get back to you.

Michael
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Re: Computational Fluid Dynamics (CFD) workbench using OpenFOAM

Postby Crossleyuk » Thu Jul 18, 2019 8:23 am

I realised this wasn't the place for this so I have now posted on a forum page named "Crash when I open a file" but this was my original question. No response from other forum post yet.

Things have moved on fantastically well now and I have a full FreeCAD and CFD model together with understanding, great interest and a way forward.

Latest problem is very strange. Both FreeCAD and ParaView have plain stopped working. ParaView will not start at all and FreeCAD will not open a file. I get the FreeCAD introductory screen, but it fails as soon as I select a case file. Neither are shown in my Task Manager.

Sure it's me looking for quick help but do you have any suggestions? After some unsuccessful web searches thought is to uninstall both and try again.

Thanks again all!! And fingers crossed.

Michael
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Re: Computational Fluid Dynamics (CFD) workbench using OpenFOAM

Postby oliveroxtoby » Fri Jul 19, 2019 9:16 am

Crossleyuk wrote:
Thu Jul 18, 2019 8:23 am
I realised this wasn't the place for this so I have now posted on a forum page named "Crash when I open a file" but this was my original question. No response from other forum post yet.

Things have moved on fantastically well now and I have a full FreeCAD and CFD model together with understanding, great interest and a way forward.

Latest problem is very strange. Both FreeCAD and ParaView have plain stopped working. ParaView will not start at all and FreeCAD will not open a file. I get the FreeCAD introductory screen, but it fails as soon as I select a case file. Neither are shown in my Task Manager.

Sure it's me looking for quick help but do you have any suggestions? After some unsuccessful web searches thought is to uninstall both and try again.

Thanks again all!! And fingers crossed.

Michael
Have a look at https://forum.freecadweb.org/viewtopic. ... 7ab20f7a19 - are you trying to load a file created with an older version of CfdOF, perhaps? This might cause FreeCAD to crash.
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Re: Computational Fluid Dynamics (CFD) workbench using OpenFOAM

Postby Crossleyuk » Fri Jul 19, 2019 11:52 am

"Have a look at https://forum.freecadweb.org/viewtopic. ... 7ab20f7a19 - are you trying to load a file created with an older version of CfdOF, perhaps? This might cause FreeCAD to crash."

Thanks, yes Oliver, I looked at that earlier and posted there. I don't recollect the CfdOF update but see from your other post that one has recently been made. This makes sence, the file was created weeks ago and I've used it regularly until a recent break.

You said, "If you need to get at the old version to load your existing files, this can be done with the 'v0' tag in the git repository." and I understand but I have no idea how to use the git repository. Are you suggesting that the old CfdOF is still available or are you suggesting I can save it again to use in the revised CfdOF?

Sorry stiil a LOT to learn about the details of FreeCAD and Paraview.

Many thanks again.

Michael
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Re: Computational Fluid Dynamics (CFD) workbench using OpenFOAM

Postby oliveroxtoby » Fri Jul 19, 2019 7:17 pm

Crossleyuk wrote:
Fri Jul 19, 2019 11:52 am
"Have a look at https://forum.freecadweb.org/viewtopic. ... 7ab20f7a19 - are you trying to load a file created with an older version of CfdOF, perhaps? This might cause FreeCAD to crash."

Thanks, yes Oliver, I looked at that earlier and posted there. I don't recollect the CfdOF update but see from your other post that one has recently been made. This makes sence, the file was created weeks ago and I've used it regularly until a recent break.

You said, "If you need to get at the old version to load your existing files, this can be done with the 'v0' tag in the git repository." and I understand but I have no idea how to use the git repository. Are you suggesting that the old CfdOF is still available or are you suggesting I can save it again to use in the revised CfdOF?

Sorry stiil a LOT to learn about the details of FreeCAD and Paraview.

Many thanks again.

Michael
I have posted an explanation in reply to your other message. Of course this would only explain difficulty in opening files which have CfdOF objects in them, and it doesn't explain your paraview problem.

If you are running the AppImage on Linux, there can sometimes be issues starting Paraview from within the workbench, but you should still be able to run it from outside FreeCAD if this is the case.
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Re: Computational Fluid Dynamics (CFD) workbench using OpenFOAM

Postby Crossleyuk » Mon Jul 29, 2019 8:16 am

Hi again Oliver and ALL!

So as I tried to explain on my final "crash when I open a file" forum topic post, I think I've overcome my FreeCAD loading failure problems. But I now have problems understanding my rebuilt CFD model in FC 0.18. I wanted to start by posting my new FC 0.18 model but I'm getting a "file too large" error (2.39MB) but it's just a repeat of the same FC 0.17 model that I've posted before. I get the following error when I run CfdSolver.
Analysis Control Failure July 29th.PNG
Analysis Control Failure July 29th.PNG (19.73 KiB) Viewed 101 times

I'll continue to try and understand what's happening but is there any other way I can get the model to you please.

Many thanks again!

Michael