Observing a Recirculated Flow Proximal to a Constriction

ashtonJ · April 1, 2014, 00:17

Dear all,
I am modelling flow in an artery, which is initially (t = 0 s) unimpeded, then starts to narrow to form a constriction (t = 0.4 s) and finally returns to its initial non-constricted state (t=1 s). I use pressure waveform as inlet boundary condition and axial velocity waveform as outlet boundary condition (please see the attachment).

I have observed a recirculated flow proximal to the constriction experimentally, however, the modelling results do not predict that recirculation! The problem might be because of boundary conditions!!
Does anyone know what boundary condition could predict a recirculated flow proximal to the constriction?

Regards,
AshtonJ

ghorrocks · April 1, 2014, 18:20

No images are attached.

Have you done all the normal accuracy checks? http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

ashtonJ · April 1, 2014, 19:52

Dear ghorrocks,
Yes, I've done grid dependency and error analysis test.
My question is whether observing a recirculation proximal to a stenosis is possible from CFD point of view? If yes, please let me know the physical condition under which it happens.
Actually, I have not come across this before. Thanks

ghorrocks · April 1, 2014, 20:08

Can you post an image of what you are seeing?

ashtonJ · April 1, 2014, 20:28

Please the following image:

As seen, a recirculated flow region is observed in pre-stenosis region.

ghorrocks · April 1, 2014, 20:43

Strange - the email notification included the link but the web forum has stripped it. I don't know what it happening there.

Anyway, I have seen the picture now. It looks unusual and you would need unusual circumstances to make that come about. It is possible that it is caused by inadequate convergence, but it could also be caused by your boundary conditions. You would have to do some post processing to work that out.

ashtonJ · April 1, 2014, 20:47

Actually, I've seen that pre-stenosis recirculation experimentally, I want to create the same thing by CFD ...

ghorrocks · April 1, 2014, 20:49

Sure, but if the recirculation occurs right next to your boundary condition I would be very suspicious of it. You want to make sure important flow stuff happens well away from your boundary conditions. So you might need to move your upstream boundary condition further upstream.

ashtonJ · April 1, 2014, 20:58

It does not happen next to the boundary, it is far from inlet. In my laboratory experiment, in a 600 mm Pipe, a recirculation was observed 150 mm far from inlet and 100 mm far from beginning of stenosis.

ghorrocks · April 1, 2014, 22:09

If your boundary condition has the flow going in one direction then stops it and reverses the direction this can cause recirculations.

April 1, 2014, 00:17	Observing a Recirculated Flow Proximal to a Constriction	#1
ashtonJ Senior Member Ashkan Javadzadegan Join Date: Sep 2010 Posts: 255 Rep Power: 16	Dear all, I am modelling flow in an artery, which is initially (t = 0 s) unimpeded, then starts to narrow to form a constriction (t = 0.4 s) and finally returns to its initial non-constricted state (t=1 s). I use pressure waveform as inlet boundary condition and axial velocity waveform as outlet boundary condition (please see the attachment). I have observed a recirculated flow proximal to the constriction experimentally, however, the modelling results do not predict that recirculation! The problem might be because of boundary conditions!! Does anyone know what boundary condition could predict a recirculated flow proximal to the constriction? Regards, AshtonJ

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April 1, 2014, 18:20		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	No images are attached. Have you done all the normal accuracy checks? http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

April 1, 2014, 19:52		#3
ashtonJ Senior Member Ashkan Javadzadegan Join Date: Sep 2010 Posts: 255 Rep Power: 16	Dear ghorrocks, Yes, I've done grid dependency and error analysis test. My question is whether observing a recirculation proximal to a stenosis is possible from CFD point of view? If yes, please let me know the physical condition under which it happens. Actually, I have not come across this before. Thanks

April 1, 2014, 20:08		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	Can you post an image of what you are seeing?

April 1, 2014, 20:28		#5
ashtonJ Senior Member Ashkan Javadzadegan Join Date: Sep 2010 Posts: 255 Rep Power: 16	Please the following image: As seen, a recirculated flow region is observed in pre-stenosis region.

April 1, 2014, 20:43		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	Strange - the email notification included the link but the web forum has stripped it. I don't know what it happening there. Anyway, I have seen the picture now. It looks unusual and you would need unusual circumstances to make that come about. It is possible that it is caused by inadequate convergence, but it could also be caused by your boundary conditions. You would have to do some post processing to work that out.

April 1, 2014, 20:47		#7
ashtonJ Senior Member Ashkan Javadzadegan Join Date: Sep 2010 Posts: 255 Rep Power: 16	Actually, I've seen that pre-stenosis recirculation experimentally, I want to create the same thing by CFD ...

April 1, 2014, 20:49		#8
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	Sure, but if the recirculation occurs right next to your boundary condition I would be very suspicious of it. You want to make sure important flow stuff happens well away from your boundary conditions. So you might need to move your upstream boundary condition further upstream.

April 1, 2014, 20:58		#9
ashtonJ Senior Member Ashkan Javadzadegan Join Date: Sep 2010 Posts: 255 Rep Power: 16	It does not happen next to the boundary, it is far from inlet. In my laboratory experiment, in a 600 mm Pipe, a recirculation was observed 150 mm far from inlet and 100 mm far from beginning of stenosis.

April 1, 2014, 22:09		#10
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	If your boundary condition has the flow going in one direction then stops it and reverses the direction this can cause recirculations.