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 )

Moderator: oliveroxtoby

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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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oliveroxtoby
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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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Crossleyuk
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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