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-   -   How can I used cyclic BC in icoFoam? (http://www.cfd-online.com/Forums/openfoam/69255-how-can-i-used-cyclic-bc-icofoam.html)

sai October 16, 2009 16:56

How can I used cyclic BC in icoFoam?
 
Hi, I'm trying to simulate a laminar flow trough a pipe with icoFoam using cyclic BC on the inlet and outlet of the tube. I want to impose the pressure gradient between the faces but I can't. It seems like the cyclic condition doesn't accept another condition.
I would like to find an way to impose the pressure gradient and mantain the cyclic condition between the inlet and outlet of the tube.

Thanks

santos October 17, 2009 04:58

Hi,

I dont think icoFoam allows the use of cyclics. You can use instead channelFoam and switch LESModel to laminar in LESProperties.

Regards,
Jose Santos

alberto October 17, 2009 16:25

icoFoam allows cyclic BC's to be used, but it has not mechanism to impose a fixed pressure gradient.

To do that you need to add your constant pressure gradient at the momentum equation. channelFoam imposes a fixed flow rate.

Best,

milleniumrider November 12, 2009 10:14

hi i'd like some more information on what you suggested
 
Hi Alberto,

Can you elaborate a little on what you said. Constant pressure gradient, in icoFoam?

I'm sorry if this is an extremely basic question, I've just started CFD and am still grappling my way through.

Any help or explanation would be much appreciated.

Thanks,
Vasu

alberto November 12, 2009 21:54

Quote:

Originally Posted by milleniumrider (Post 236000)
Hi Alberto,

Can you elaborate a little on what you said. Constant pressure gradient, in icoFoam?

I'm sorry if this is an extremely basic question, I've just started CFD and am still grappling my way through.

Any help or explanation would be much appreciated.

Thanks,
Vasu

Hi Vasu,

I meant that if you use cyclic boundary conditions in a pipe with icoFOAM, assuming you give an initial non-zero velocity to the flow, you will notice, if you use the code as is, that the fluid slows down in time due to the effect of the wall.

If you want to compute a flow with a constant mean mass flow rate or a constant pressure gradient between inlet and outlet you need to change the code.

If you want to impose a constant pressure gradient, all you have to do is adding it to the momentum equation. If you want to impose a constant mass flow rate, you need to do something similar to what is done in channelFoam.

Best,

milleniumrider November 13, 2009 06:33

[QUOTE=alberto;236071]Hi Vasu,

I meant that if you use cyclic boundary conditions in a pipe with icoFOAM, assuming you give an initial non-zero velocity to the flow, you will notice, if you use the code as is, that the fluid slows down in time due to the effect of the wall.

Yep thankfully thats what happens.

If you want to compute a flow with a constant mean mass flow rate or a constant pressure gradient between inlet and outlet you need to change the code.

If you want to impose a constant pressure gradient, all you have to do is adding it to the momentum equation. If you want to impose a constant mass flow rate, you need to do something similar to what is done in channelFoam.


Ok I think I understand. I've been comparing it with the channelFoam case to try to understand better. I'll give it a shot and see how it goes.
Thanks for the help!
Cheers,
Vasu

cmh July 4, 2013 05:46

Quote:

Originally Posted by alberto (Post 236071)
Hi Vasu,

I meant that if you use cyclic boundary conditions in a pipe with icoFOAM, assuming you give an initial non-zero velocity to the flow, you will notice, if you use the code as is, that the fluid slows down in time due to the effect of the wall.

If you want to compute a flow with a constant mean mass flow rate or a constant pressure gradient between inlet and outlet you need to change the code.

If you want to impose a constant pressure gradient, all you have to do is adding it to the momentum equation. If you want to impose a constant mass flow rate, you need to do something similar to what is done in channelFoam.

Best,


HI Alberto,

Newbie alert.

Anyhow how do I modify the code in Icofoam such that i can provide the pressure gradient at the inlet and the outlet to calculate the velocity?

Regards


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