Laminate flow through a tube with unexpected turbulence

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 September 15, 2008, 05:33 Hello OpenFoam User, I have #1 New Member   Volker Ludewig Join Date: Mar 2009 Location: Chemnitz, saxony, germany Posts: 12 Rep Power: 8 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

 September 15, 2008, 10:15 Hi again, Laminate should b #2 New Member   Volker Ludewig Join Date: Mar 2009 Location: Chemnitz, saxony, germany Posts: 12 Rep Power: 8 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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