Learning Forum

[Lucien Kuhn]

Hi,

I am trying to simulate a situation in which a sample of the fluid is taken during the simulation. My goal is to have the second pressure outlet open time-shifted after a short delay in which I give the flow time to fully form. From what I have researched my best guess at an attempt would be to utilise UDFs for this issue but I have trouble formulating the correct code and implementing it.

I would like to provide a picture of the geometry but I have trouble uploading the image. The geometry is a simple flow channel with a short branch with the sample pressure outlet. So I aim to just get the hang of it with a very simple geometry so I can apply it to more complex problems.

Thanks in advance to everyone taking the time of day to provide me with some aid.

Best regards,

Lucien

[Rob]

If you're using a flow boundary you want DEFINE_PROFILE   I suspect a velocity boundary with negative value might be a better option? 

[Lucien Kuhn]

Hi Rob, thanks for the fast reply!

I am quite new to ANSYS in general, so I am not certain I understand your response correctly. My idea was to create a UDF that would change the sample outlet surface from wall to pressure outlet after a set amount of time after starting the simulation. But since I am new I don't know if that's even the correct approach. And regarding your response, would a negative value make it cancel out the incoming flow creating a boundary for the time the sample is supposed to be closed in the beginning?

[Rob]

Have a look at the various courses in Learning, and also the tutorials in Help. 

Re the sample, do you want to set a pressure, or fixed flow out of the domain? Sketch out the model along with all known (and needed) data to better understand what you want from the model. Ie treat simulation as you would an experiment. 

[Lucien Kuhn]

Thanks for the replies. Can you by any chance refer me to said Tutorials because I have yet to find one that truly helped me. (I was wishing for someone to tell me how to do it here, but if I can get a nice tutorial, I won't be complaining)

[Rob]

You'll not find a tutorial with exactly what you want. Do all of the single phase ones, it's good practice too. That will show you what the various boundary conditions are, and once you've got a model you can experiment. 

We're here to help you learn, and that's not always by answering your question! 

[Lucien Kuhn]

Thanks for the reply! I understand but I am a bit limited in terms of time because I am in the middle of my bachelor thesis and no one of the PhD candidates have any experience with UDFs so I turned to this forum in hopes for somewhat specific guide lines if not the exact solution to my problem.

[Rob]

There's a DEFINE_PROFILE example in the manual, and https://ansyshelp.ansys.com/account/Secured?returnurl=/Views/Secured/corp/v241/en/flu_udf/flu_udf_ModelSpecificDEFINE.html%23x1-1800003.3.17 Section 2.3.30.10 has the time macro you'll need.  

[Lucien Kuhn]

Thanks Rob! I have been trying to find a way to open the link because if I copy it I have to register and I cannot find my account number and no presented way of obtaining it has been working (I have ANSYS Student Version). So my question is: Can I manually find said thread and section?

[Rob]

Open Help in Fluent & copy the link into that browser.