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Observing a Recirculated Flow Proximal to a Constriction

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Old   April 1, 2014, 00:17
Question Observing a Recirculated Flow Proximal to a Constriction
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Ashkan Javadzadegan
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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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Old   April 1, 2014, 18:20
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Glenn Horrocks
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No images are attached.

Have you done all the normal accuracy checks? http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F
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Old   April 1, 2014, 19:52
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Ashkan Javadzadegan
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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
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Old   April 1, 2014, 20:08
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Can you post an image of what you are seeing?
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Old   April 1, 2014, 20:28
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Ashkan Javadzadegan
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Please the following image:

As seen, a recirculated flow region is observed in pre-stenosis region.
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Old   April 1, 2014, 20:43
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Glenn Horrocks
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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.
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Old   April 1, 2014, 20:47
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Actually, I've seen that pre-stenosis recirculation experimentally, I want to create the same thing by CFD ...
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Old   April 1, 2014, 20:49
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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.
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Old   April 1, 2014, 20:58
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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.
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Old   April 1, 2014, 22:09
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If your boundary condition has the flow going in one direction then stops it and reverses the direction this can cause recirculations.
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