|
[Sponsors] |
Help--how to define outlet boundary condition? |
|
LinkBack | Thread Tools | Search this Thread | Display Modes |
May 24, 2012, 17:12 |
Help--how to define outlet boundary condition?
|
#1 |
New Member
guoji xu
Join Date: Feb 2012
Posts: 19
Rep Power: 14 |
Hi,everyone. I want to simulate 2 D Stokes wave using fluent 13, the result is shown in the picture. In this picture, several waves are good in the first half of flume, but at the second half of the flume, the waves dissipate so rapidly. I don't know why. I am wondering should I define a pressure profile udf to define the outlet? Could anybody give some advice? Thanks in advance! |
|
May 25, 2012, 02:45 |
|
#2 |
Member
James Willie
Join Date: Mar 2009
Posts: 81
Rep Power: 17 |
Hi, Can you throw more light on your problem? Like is the flow turbulent? I would assume no? and did you introduce any disturbance at the inlet in the velocity, etc? Jimmy
|
|
May 25, 2012, 09:47 |
|
#3 | |
New Member
guoji xu
Join Date: Feb 2012
Posts: 19
Rep Power: 14 |
Quote:
Actually, the flow is laminar flow, without any turbulent at the inlet velocity profile. the boudary conditions are velocity inlet, bottom--no slipping wall, top--no slipping wall, outlet--out flow. Should I define a pressure udf for the out flow? Thank you very much again. |
||
May 25, 2012, 10:52 |
|
#4 |
Member
James Willie
Join Date: Mar 2009
Posts: 81
Rep Power: 17 |
It means u defined a velocity profile at the inlet? Am I getting you right? If yes, then you need to just need to increase the amplitude of the disturbance or flutuation in your velocity profile. The code is probably damping the wave and this is likely numerical. Make sure you do grid dependency test to remove any ambiguity. Jimmy
|
|
May 25, 2012, 11:05 |
|
#5 | |
New Member
guoji xu
Join Date: Feb 2012
Posts: 19
Rep Power: 14 |
Quote:
Thank you, Jimmy! |
||
May 28, 2012, 06:41 |
|
#6 |
Member
James Willie
Join Date: Mar 2009
Posts: 81
Rep Power: 17 |
Hi, is your profile at the inlet a function? sin or cosine? and if yes, what is the amplitude? I suspect the amplitude is not large enough and so it is being damped? so play with that and see. because you are using the euler euqation, we should not have any damping due to viscous effects. If there is then it is numerical. That is why i am asking about whether you did any grid dependency test? Jimmy
|
|
May 28, 2012, 07:33 |
|
#7 |
Member
Daniel Tanner
Join Date: Apr 2009
Posts: 54
Rep Power: 17 |
Might be worth trying the pressure outlet boundary condition (instead of the outflow condition). The outflow condition may not be suitable for this application (it assumes fully developed conditions at the outlet).
|
|
May 28, 2012, 11:16 |
|
#8 | |
New Member
guoji xu
Join Date: Feb 2012
Posts: 19
Rep Power: 14 |
Quote:
One small question, could you explain what is grid dependency test? you mean try different grid meshing? Thank you very much! Happy Memorial Day! |
||
May 28, 2012, 11:22 |
|
#9 |
New Member
guoji xu
Join Date: Feb 2012
Posts: 19
Rep Power: 14 |
||
May 28, 2012, 11:23 |
|
#10 |
Member
James Willie
Join Date: Mar 2009
Posts: 81
Rep Power: 17 |
Hi, And thanks for the wishes. About grid dependency test. You have a case where the waves you have in your flow are dissipating quickly than expected. The qauestions is is it physical or non-phsical or numerical? To remove the third case, you try have to do grid dependency test. Like you said you need to vary your mesh resolution till you have no change in your critical variable of interest. It could be the pressure or velocity or temperature in a given section or boundary of your flow. When that happens, you can reliably say that the results you are getting are void of any numerical artifacts and therefore must be due to the physics of the flow. In the case you have right now it would be difficult to say. Good luck! James
|
|
May 28, 2012, 11:26 |
|
#11 | |
Senior Member
Rick
Join Date: Oct 2010
Posts: 1,016
Rep Power: 26 |
Quote:
Daniele EDIT: ok, jwillie was faster |
||
May 28, 2012, 11:40 |
|
#12 | |
New Member
guoji xu
Join Date: Feb 2012
Posts: 19
Rep Power: 14 |
Quote:
|
||
May 28, 2012, 11:41 |
|
#13 |
New Member
guoji xu
Join Date: Feb 2012
Posts: 19
Rep Power: 14 |
Thank you for your kind-hearted reply. May God bless you!
|
|
May 28, 2012, 13:15 |
|
#14 |
Member
James Willie
Join Date: Mar 2009
Posts: 81
Rep Power: 17 |
Hi, Not sure if your question is already answered about physical or non-physical? Physical is whether the phenomenon you are observing or your results can be attributed to physics or reality or not. Some of them are numerical or non-physical...meaning it cannot be attributed to physics and sometimes simply does not hold. Hope it helps. Jimmy
|
|
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Wind turbine simulation | Saturn | CFX | 58 | July 3, 2020 01:13 |
How to set the Heat Flux boundary condition at Outlet | creddy_trddc | CFX | 3 | September 21, 2011 07:44 |
Setting outlet Pressure boundary condition using CAFFA code | Mukund Pondkule | Main CFD Forum | 0 | March 16, 2011 03:23 |
define boundary condition in just one cell face | om1234 | Fluent UDF and Scheme Programming | 0 | June 16, 2010 19:11 |