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Laminate flow through a tube with unexpected turbulence

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Old   September 15, 2008, 05:33
Default Hello OpenFoam User, I have
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Volker Ludewig
Join Date: Mar 2009
Location: Chemnitz, saxony, germany
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Hello OpenFoam User,

I have a big problem:

I have simulated the laminate flow through a valve and the results were in an expected area.
I was happy.

The last weekend I tried to validate the results with a very simple shape: a tube with the same boundary conditions as for the valve.
The pictures of the results seem like pictures of modern art: red and blue spots on a green ground.
Some vectors of the flow are going back or are orientated to the wall.

The Courant no. was increasing after the second loop above 1 and climbed up to 100.000 and above in the 4th loop.
The number of Iteration steps reached 1001.

Tube dimension: length 1m, diameter 0.2m
v=1m/s
nu=0.05m^2/s (similar to sewage sludge)
density= 1200kg/m^3
Reynoldnr Re=4<2300->should be laminar
Expected pressure difference between inlet and outlet: 40 Pa/Density (simulated between -1.E28 and 1.E37 ???)

I applied IcoFoam.
Mesh: 68,000 tetrahedrons produced with Salome meca.

Time step: 0.1 s, End time 0.6s.

Who can help me??
I apologize for my bad English.

Kind regards
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Old   September 15, 2008, 10:15
Default Hi again, Laminate should b
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Volker Ludewig
Join Date: Mar 2009
Location: Chemnitz, saxony, germany
Posts: 12
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Hi again,

Laminate should be laminar :-)

Could it be, that the time steps are to long ??
I found into the user guide following equation:
(at page U25)

Co x Deltax / v = max. time step

recommented time steps: min. 10 times
Co- Courant Number-> should be less than 1
Deltax- min. is the cell size in the direction of the velocity
v- expected magnitude of Velocity

Is the question correct interpreted??
What about number of recommented time steps??
is 10 times to few or only guilty for laminar flow ??

Kind regards
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