Profile Boundary conditions

diamondx · January 16, 2013, 14:34

Dear cfd-onliners,
I'm about to start my master degree, in some cases i might divide my simulation into two cases, and use an outlet region as an inlet condition in a new analysis. i have always been curious about this method since i'm not sure it can work correctly because:

When you perform a simulation with the first case, the OUTLET used, geometrically speaking, should be extended a little (right ?), otherwise problems with convergence will occur, and error like the reversed flow warning, or just because i often hear "OUTLET should be big"

If we extend the outlet, how should it be extended ? the first thing my mind come up with is to include a similar and simplified second case. why ? so we can respect and well anticipate the flow behavior...

The other way is to just add a big domain as outlet... if we do that, i'm not sure our variable in the outlet (velocity,pressure,temperature) will be correct. Why ?
In my aerodynamic class, i always learned that the flow follow a certain path-line, when doing external aerodynamics study of car for example, my teacher used to tell me the particle pushes the one behind it and it continues like that, hence the flow deviate around the car. SO what's next really implies change to the upstream...

i hope i was enough clear, really sorry for this long explanation. hoping i can get some help.

Thanks a lot in advance,

ghorrocks · January 16, 2013, 16:48

The outlet should not be big. In fact it is often easier when the outlet is small. But the outlet should be far enough downstream to not affect the results of the area being modelled, and not have any recirculations going through it.

The best way to do this extension of the outlet is by modelling whatever is actually downstream in the system you are modelling. If it is a long pipe then model more of the pipe. If exhausts to atmosphere, model a big atmosphere region.

January 16, 2013, 14:34	Profile Boundary conditions	#1
diamondx Super Moderator Ghazlani M. Ali Join Date: May 2011 Location: Tokyo, Japan Posts: 1,385 Blog Entries: 23 Rep Power: 28	Dear cfd-onliners, I'm about to start my master degree, in some cases i might divide my simulation into two cases, and use an outlet region as an inlet condition in a new analysis. i have always been curious about this method since i'm not sure it can work correctly because: When you perform a simulation with the first case, the OUTLET used, geometrically speaking, should be extended a little (right ?), otherwise problems with convergence will occur, and error like the reversed flow warning, or just because i often hear "OUTLET should be big" If we extend the outlet, how should it be extended ? the first thing my mind come up with is to include a similar and simplified second case. why ? so we can respect and well anticipate the flow behavior... The other way is to just add a big domain as outlet... if we do that, i'm not sure our variable in the outlet (velocity,pressure,temperature) will be correct. Why ? In my aerodynamic class, i always learned that the flow follow a certain path-line, when doing external aerodynamics study of car for example, my teacher used to tell me the particle pushes the one behind it and it continues like that, hence the flow deviate around the car. SO what's next really implies change to the upstream... i hope i was enough clear, really sorry for this long explanation. hoping i can get some help. Thanks a lot in advance, __________________ Regards, New to ICEM CFD, try this document --> https://goo.gl/KAOIwm Ali

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
non reflective boundary conditions for incompresible flow	Pascal_doran	OpenFOAM Programming & Development	16	August 25, 2015 05:35
Radiation interface	hinca	CFX	15	January 26, 2014 17:11
ribbed channel / simpleFoam / boundary conditions	beeo	OpenFOAM Pre-Processing	20	July 17, 2013 08:39
An error has occurred in cfx5solve:	volo87	CFX	5	June 14, 2013 17:44
[Netgen] boundary conditions and mesh exporting	vaina74	OpenFOAM Meshing & Mesh Conversion	2	May 27, 2010 09:38

January 16, 2013, 16:48		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	The outlet should not be big. In fact it is often easier when the outlet is small. But the outlet should be far enough downstream to not affect the results of the area being modelled, and not have any recirculations going through it. The best way to do this extension of the outlet is by modelling whatever is actually downstream in the system you are modelling. If it is a long pipe then model more of the pipe. If exhausts to atmosphere, model a big atmosphere region.