Learning Forum

[CMCsupport1]

Good afternoon,

 

One of our student subscribers has encountered the following problem. He is using ANSYS 19.2, accessing our 'Campus Solutions' licence, and has looked over related examples and tutorials for help. Here is his description:

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I have a duct that instead of inlet and outlet I've put the periodic boundary condition with a mass flow rate which indicates that this duct is infinite. Everything is ok except for pressure drop. The contour is messed up. I asked my friends;  they ran it with a different version of Ansys Fluent but it didn't work. One of my friends ran it with Fluent 6.3 and could get the right answers. Can you help me how to get good pressure drop and contours?

(I should note that Ansys is ok, and I have already read the Fluent tutorial and help. I already searched the web and forums. If you have other suggestions. Please help me)

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We can attach/embed a copy of the contour plot to illustrate his difficulty, and will try now.

 

[CMCsupport1]

[Rob]

Check material properties (all constant) and the mesh quality (if it's not the same mesh as used in v6.3).  Using a pressure drop is more stable, but mass flow should work (and does - I've been running a case). Try initialising the flow to the calculated velocity, otherwise I'm a bit stuck as I can't take the files. 

[CMCsupport1]

Good morning,

Thank you for your prompt response. We've pointed our student user to your reply.

 

Regards,

CMC Microsystems' technical support staff

 

 

[sumykk]

Hi, 

Thanks For your prompt answer. Material properties are all constant and mesh quality is good (simple structured 2D mesh and the flow is laminar). 

I'll check the initialization. 

Can I ask what is your Ansys version? 

Thanks

[sumykk]

And I should note that the results are correct, even the pressure drop. But the contour of pressure is as messy as you can see.

Thanks again.

[DrAmine]

Tue Contour of pressure is referring to the part of pressure which for the flow passage. This pressurw field will repeat itsekf reduced by the linear pressure drop to the end.

[sumykk]

Hi Amine, 

It's a flow between 2 parallel plates. As we know in a fully developed region (which it is in our case due to the choice of periodic boundary condition with mass flow rate instead of inlet and outlet) in such a flow the pressure drop is linear, but if you pay attention to the contour you can easily see that it's chaotic and random pressure distribution. 

 

Bests 

Ali 

[DrAmine]

Again that is not the real pressure what you are looking into that is just the part left after removing the periodic linear pattern.

[sumykk]

Thank you Amine for the answer, How can I look into the real pressure? 

 

Bests,

Ali

 

[DrAmine]

as a rough estimate: dp/dx times the length of the passe + gauge pressure is the "real" gauge pressure for the passage.

[sumykk]

Thanks! How can I get the contour of the real pressure drop? because I want to model a pipe with some obstacle inside and see the contour of pressure, which on that case the pressure drop is not as simple as dp/dx*length, because dp/dx is not constant anymore. 

 

Bests,

Ali

[CMCsupport1]

Good afternoon,

If there is a relevant example we could retrieve for this student from behind your portal, please point us to it. Alternately, there must be a pertinent tutorial in your collection somewhere? ANSYS staff never lets us down.

Fingers crossed.

[DrAmine]

Good idea to create a small example.

[sumykk]

Thanks! If that's possible I'll be more than happy because I didn't get a satisfying answer.

 

Bests,

Ali

[DrAmine]

Whenever this is done it will be published on the portal. But all of you can do similar by creating a small example and compare it to theoretical pressure drop.

[sumykk]

Thanks!

[CMCsupport1]

Good afternoon,

CMC staff will close this case today, as this student is comfortable using your Community resources for himself.

Thank you for your advice.