Problem with multidomain interface

jzapatau · August 20, 2014, 23:50

Sory for the interruption, I'm getting started with ansys cfx and I've been having lots of trouble with modeling a sudden high pressure vessel discharge into atmosphere.
What I've done so far is to create a multibody part in DM, then mesh it in the Ansys Meshing program with a sweep method, making sure that mesh is conformal between my two bodies (tank and discharge zone) and later set in the Pre two domains with an interface between them and each of them with their corrsponding initialization.
The problem arises when I get to Post and find that there is no mass flow between domains, as if there was no discharge, and abs. pressures remains the same.
I'd appreciate any answer, and sory again for the interruption.

ghorrocks · August 21, 2014, 05:58

No need to apologise for the interruption, the forum is here to ask questions.

It sounds like you have not applied your interface correctly, so the two domains are not connected. In fact there is no reason to do this as a multidomain problem, it can easily be done as a single domain with an initial condition. Then you do not need interfaces (which is slightly preferable, there is a small computing overhead in including interfaces).

jzapatau · August 21, 2014, 09:40

First of all, thanks for your reply Glenn.

Ok, I thought I needed two domains due to distinct initial conditions between them (one at high pressure and the other one at atmosphere conditions). Then, if the problem can be solved using a single domain, how do I set the different initial pressures between the two regions of the domain?

Opaque · August 21, 2014, 10:04

Relative Pressure = High Pressure * inside()@Volume 1 + Low Pressure * inside()@Volume 2

the inside()@Location is 1 within the location, and 0 elsewhere.

jzapatau · August 21, 2014, 10:10

Brilliant!!!

Do you know about any good manual from where I can learn that syntax?

ghorrocks · August 21, 2014, 20:38

The CFX Reference manual, in the section on Variables, functions and CEL.

jzapatau · August 22, 2014, 19:26

Thank you Glenn,

Now I've done what you've told me but again I'm having the same problem. I got rid of the interface and instead applied a single domain with different pressures at the initialization.

Mesh seems to be conformal as in the connectivity icon of the Pre both faces appear as a 1:1 connection. Maybe there's a parameter I'm totally unaware of that's making this section to work as a wall, but I've double checked it.
Also it's kind of weird that in the Post the streamlines are drawn in the particular way I expect the flow to discharge though the colorbar tells me the velocity value is almost zero (frustrating when I'm expecting supersonic flow at discharge area).

Thanks again!

August 20, 2014, 23:50	Problem with multidomain interface	#1
jzapatau New Member José Join Date: May 2014 Location: Argentina Posts: 7 Rep Power: 11	Sory for the interruption, I'm getting started with ansys cfx and I've been having lots of trouble with modeling a sudden high pressure vessel discharge into atmosphere. What I've done so far is to create a multibody part in DM, then mesh it in the Ansys Meshing program with a sweep method, making sure that mesh is conformal between my two bodies (tank and discharge zone) and later set in the Pre two domains with an interface between them and each of them with their corrsponding initialization. The problem arises when I get to Post and find that there is no mass flow between domains, as if there was no discharge, and abs. pressures remains the same. I'd appreciate any answer, and sory again for the interruption.

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August 21, 2014, 05:58		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	No need to apologise for the interruption, the forum is here to ask questions. It sounds like you have not applied your interface correctly, so the two domains are not connected. In fact there is no reason to do this as a multidomain problem, it can easily be done as a single domain with an initial condition. Then you do not need interfaces (which is slightly preferable, there is a small computing overhead in including interfaces).

August 21, 2014, 09:40		#3
jzapatau New Member José Join Date: May 2014 Location: Argentina Posts: 7 Rep Power: 11	First of all, thanks for your reply Glenn. Ok, I thought I needed two domains due to distinct initial conditions between them (one at high pressure and the other one at atmosphere conditions). Then, if the problem can be solved using a single domain, how do I set the different initial pressures between the two regions of the domain?

August 21, 2014, 10:04		#4
Opaque Senior Member Join Date: Jun 2009 Posts: 1,804 Rep Power: 32	Relative Pressure = High Pressure * inside()@Volume 1 + Low Pressure * inside()@Volume 2 the inside()@Location is 1 within the location, and 0 elsewhere.

August 21, 2014, 10:10		#5
jzapatau New Member José Join Date: May 2014 Location: Argentina Posts: 7 Rep Power: 11	Brilliant!!! Do you know about any good manual from where I can learn that syntax?

August 21, 2014, 20:38		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	The CFX Reference manual, in the section on Variables, functions and CEL.

August 22, 2014, 19:26		#7
jzapatau New Member José Join Date: May 2014 Location: Argentina Posts: 7 Rep Power: 11	Thank you Glenn, Now I've done what you've told me but again I'm having the same problem. I got rid of the interface and instead applied a single domain with different pressures at the initialization. Mesh seems to be conformal as in the connectivity icon of the Pre both faces appear as a 1:1 connection. Maybe there's a parameter I'm totally unaware of that's making this section to work as a wall, but I've double checked it. Also it's kind of weird that in the Post the streamlines are drawn in the particular way I expect the flow to discharge though the colorbar tells me the velocity value is almost zero (frustrating when I'm expecting supersonic flow at discharge area). Thanks again!