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How to use periodic flow condition under single phase laminar flow

Posted 19 avr. 2012, 21:37 UTC−4 2 Replies

Dan Linard
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Hi,

I am confused on how to use the periodic flow condition. I have a long and repeated geometry, and I want to model just one section of it (since it is repeated anyway).

Attached is a very simple geometry. My goal is to have the flow coming out of the outlet and go back into the inlet x-number of times.

Right now, the settings I have are: Incompressible flow, and a pressure drop of 10[pa].

However, how do I specify initial conditions at the inlet, and how do I set the number of iterations (or periods) where the outlet flow goes back into inlet flow?

Alternatively, if the above doesn't work or does not make sense, how do I take the velocity at the outlet and use it as the inlet?
2 Replies Last Post 14 sept. 2016, 14:41 UTC−4
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Hello Dan Linard

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Shawkat
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Posted: 8 years ago 14 sept. 2016, 13:39 UTC−4

Hi,

have you managed to do it in the end? I am looking to do a similar thing, but I have no idea how to go about it. I am looking for laminar flow, stationary model.
--
MSH
Hi, have you managed to do it in the end? I am looking to do a similar thing, but I have no idea how to go about it. I am looking for laminar flow, stationary model. -- MSH
Walter Frei COMSOL Employee

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Posted: 8 years ago 14 sept. 2016, 14:41 UTC−4
Hello Dan,

In your modeling of periodic flow you will want to add a "Pressure Point Constraint" condition to one point on your model to gauge-fix the pressure field, because in your model as-is you are only specifying a pressure difference, and not fixing the absolute pressure. With that change, your model will solve for the stationary (time-invariant) case.
For the transient model, make sure that your boundary conditions and initial conditions are in agreement. For more details, see:
www.comsol.com/support/knowledgebase/1172/

You may also find the following articles helpful:
www.comsol.com/blogs/exploiting-periodicity-in-models-with-high-peclet-numbers/
www.comsol.com/blogs/using-general-extrusion-operators-to-model-periodic-structures/

Best Regards,
Hello Dan, In your modeling of periodic flow you will want to add a "Pressure Point Constraint" condition to one point on your model to gauge-fix the pressure field, because in your model as-is you are only specifying a pressure difference, and not fixing the absolute pressure. With that change, your model will solve for the stationary (time-invariant) case. For the transient model, make sure that your boundary conditions and initial conditions are in agreement. For more details, see: https://www.comsol.com/support/knowledgebase/1172/ You may also find the following articles helpful: https://www.comsol.com/blogs/exploiting-periodicity-in-models-with-high-peclet-numbers/ https://www.comsol.com/blogs/using-general-extrusion-operators-to-model-periodic-structures/ Best Regards,

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