Reversed flow in face XXX pressure outlet

rafash2 · August 4, 2015, 08:54

Dear colleagues,
I am trying to simulate (Fluent v14) blood flow throught a stenosed vessel whose geometry has been taken from angio MRI.
When I run the case it begins with reversed flow from the begining of simulation, but it converges finally.
But the problem is that flow follows the path as shown in the attached image.
The boundary conditions are:
- Inlet: pulsatile velocity function (UDF)
- Outlet: Gauge pressure= 12000 Pa (90 mmHg)
The mesh body sizing is 1 mm.
Could you help me with this issue please??

Thank you very much!!
Regards,

fresty · August 4, 2015, 10:52

Just wondering if you could you post more details like how your mesh looks like and probably a contour of velocity/pressure instead of streamlines.. reverse flow seems likely due to apparent high velocity i.e. low pressure at inlet and instantaneous reverse flow till momentum is established...Which flow model are you using? You must have altered the fluid material properties..?

rafash2 · August 4, 2015, 14:13

Hi fresty,

Thank you for your reply.
I attach some images with a detail os mesh, pressure contour and velocity vector from inlet to outlet.
Although velocity inlet has been provided by doctors from real values (MRI and eco doppler) I have gone down these values but result is the same.
Pressure inlet is 0, bcause I consider the outlet gauge pressure= 12000 Pa.
The flow model is laminar and viscous, and the fluid material (blood) properties are: density= 1060 Kg/m3 and a Casson model (UDF) for viscosity.
Do you know where could be the problem??
Thanks a lot!!

fresty · August 4, 2015, 16:56

Everything seems alright except the pressure boundary conditions.. I am still trying to comprehend your approach but as a first thought the 0 inlet Pressure is not fitting physically as the flow potential seems non-established throughout.. have you tried specifying the inlet pressure as 12000 Pa and outlet as '0'.. would be the same thing yeah..? But it may make a difference as the domain area is highly variant & abrupt, i would hope that this explicit assignment would force flow equilibrium.. apart from this, what exactly do you expect from the result or what is that precisely doesn't match your expected flow profile..?

fresty · August 5, 2015, 17:37

Another quick check would be to switch between outflow/opening and outlet boundary conditions...

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August 4, 2015, 10:52		#2
fresty Senior Member Join Date: Aug 2014 Location: UK Posts: 213 Rep Power: 12	Just wondering if you could you post more details like how your mesh looks like and probably a contour of velocity/pressure instead of streamlines.. reverse flow seems likely due to apparent high velocity i.e. low pressure at inlet and instantaneous reverse flow till momentum is established...Which flow model are you using? You must have altered the fluid material properties..?

August 4, 2015, 16:56		#4
fresty Senior Member Join Date: Aug 2014 Location: UK Posts: 213 Rep Power: 12	Everything seems alright except the pressure boundary conditions.. I am still trying to comprehend your approach but as a first thought the 0 inlet Pressure is not fitting physically as the flow potential seems non-established throughout.. have you tried specifying the inlet pressure as 12000 Pa and outlet as '0'.. would be the same thing yeah..? But it may make a difference as the domain area is highly variant & abrupt, i would hope that this explicit assignment would force flow equilibrium.. apart from this, what exactly do you expect from the result or what is that precisely doesn't match your expected flow profile..?

August 5, 2015, 17:37		#5
fresty Senior Member Join Date: Aug 2014 Location: UK Posts: 213 Rep Power: 12	Another quick check would be to switch between outflow/opening and outlet boundary conditions...