|
[Sponsors] |
The problem of setting the boundary condition |
![]() |
|
LinkBack | Thread Tools | Search this Thread | Display Modes |
![]() |
![]() |
#1 |
New Member
Hao
Join Date: Dec 2014
Location: Beijing, China
Posts: 6
Rep Power: 11 ![]() |
Hello everyone, I have a question about the boundary condition. There is a transient analysis about damping pressure pulsation. The model I analysis is a tube which is expanding in the middle of the tube. The inlet boundary I set is a sine function of pressure. And the outlet boundary I set is still a constant pressure. I want to solve the outlet pressure that to know the rate of pressure decay. I want to ask the outlet boundary I set is right or not. I have attached a file of my model. My English is poor, I don't know what I said is clear or not. Thank you for helping me.
![]() |
|
![]() |
![]() |
![]() |
![]() |
#2 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,816
Rep Power: 144 ![]() ![]() ![]() ![]() |
You cannot tell whether your boundary conditions are correct based on what you have said. The boundary conditions are correctly applied if the accurately model the situation in the real system at that point. In the real system what is at your inlet and outlet points?
|
|
![]() |
![]() |
![]() |
![]() |
#3 | |
New Member
Hao
Join Date: Dec 2014
Location: Beijing, China
Posts: 6
Rep Power: 11 ![]() |
Quote:
But I don't know whether the pressure boundary of the outlet can affect the monitor or not. And if the setting is right, I want to know where the monitor point to set up is reasonable. Waiting for your reply. Thank you very much. |
||
![]() |
![]() |
![]() |
![]() |
#4 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,816
Rep Power: 144 ![]() ![]() ![]() ![]() |
You are using an outlet boundary where you define the pressure and you are using the outlet pressure as the output result. Can you see the problem with this configuration?
Are you doing a compressible flow model? If not why not? Is the geometry deformable? Where does the attenuation come from? Is it just the flow losses? You need to do a lot of thinking before proceeding with this simulation. In particular: * You need to consider whether your boundary conditions reflect pressure waves and will ruin your results. * You need to think about an output result which actually measures something useful. * This model requires careful validation as it is also a transient model. |
|
![]() |
![]() |
![]() |
![]() |
#5 | |
New Member
Hao
Join Date: Dec 2014
Location: Beijing, China
Posts: 6
Rep Power: 11 ![]() |
Quote:
Now I will take your advice to have a careful deliberation. Can I extend the outlet tube to avoid the interference of the outlet boundary's reflection. Or is there other usefull measure to avoid this? I know my question may be annoying. I hope you can still give me some advices. Thank you very much. Best wishes! |
||
![]() |
![]() |
![]() |
![]() |
#6 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,816
Rep Power: 144 ![]() ![]() ![]() ![]() |
Your question is not annoying - the forum is here to help people and if it is helping you then everything is good.
The muffler in a car works by using the compressibility of the exhaust gases to absorb some frequencies. You need some form of compliance to reduce the wave. That compliance could come from compressibility of a fluid, movement of the structure or other actions. |
|
![]() |
![]() |
![]() |
![]() |
#7 | |
New Member
Hao
Join Date: Dec 2014
Location: Beijing, China
Posts: 6
Rep Power: 11 ![]() |
Quote:
|
||
![]() |
![]() |
![]() |
|
|
![]() |
||||
Thread | Thread Starter | Forum | Replies | Last Post |
inlet velocity boundary condition | murali | CFX | 5 | August 3, 2012 08:56 |
Boundary condition setting regarding turbine simulation using CFX | Lacerlacer | CFX | 11 | March 12, 2012 09:32 |
Setting outlet Pressure boundary condition using CAFFA code | Mukund Pondkule | Main CFD Forum | 0 | March 16, 2011 03:23 |
Convective Heat Transfer - Heat Exchanger | Mark | CFX | 6 | November 15, 2004 15:55 |
Periodic flow boundary condition problem | sudha | FLUENT | 3 | April 28, 2004 08:40 |