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High velocity in Laminar flow

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Old   November 3, 2016, 05:37
Default High velocity in Laminar flow
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Hi all Fluent users,

I tried searching solution to my problem in this forum but I dint get or I have missed out somewhere. PLEASE HELP!!!!!

My geometry is really small of the order of millimeters. Geometry is complex and unfortunately I cannot post any pictures due to company confidentiality. But I will try to explain as much as I can.

There is single inlet and 15 outlets. We have to optimize the design so that all 15 outlets has almost equal flow distribution. Between inlet and outlet, fluid goes around complex geometry. We expect the flow to be laminar hence I used laminar flow model. You can imagine a flow is happening in a very small space between two plates.

Meshing : ICEMCFD tetmesh. I cannot do hexahedral mesh because the geometry is very complex. Quality is around 0.3.

Boundary Conditions :

Fluid : Hydrogen Gas
Inlet : Pressure inlet : Gauge Total Pressure : 80000 pascal
Outlet : All 15 outlets : Gauge Pressure : 50000 pascal
Operating Pressure : 101325 pascal
Model : Laminar
Model is symmetric hence modelling only half with symmetric BC.

INITIALIZATION: Gauge pressure : 101325 pascal
X,Y, Z Velocity = 0m/s
Reference frame : Relative cell zone

Results :

Pressure distribution seems to be fine.
Mass flow rate at the inlets and outlets match properly . ( Whatever goes in , goes out ). Also mass flow rate is somewhat close to what we expected.

PROBLEM : Maximum Velocity magnitude across the cross section of the geometry is showing around 600m/s and thats nearly mach 2.0. Though flow distribution pattern is ok but values of max velocity magnitude is not matching.

Though pressure distribution is smooth contour, Velocity distribution is not smooth and little pixelleted. I tried changing nodes values on and off, display profiles -> projection direction in all direction but to no avail.

TRIED : I tried importing the model in CFX post but I am having same results and pixelled velocty magnitude contours.

I would like to have some thoughts on this. Please let me know if any other information you need to solve this problem. Also please post a link of any discussion if happened before.

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#fluent, #highvelocity, #laminar

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