simple 3D pipe flow diverges with icoFoam
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Hello!
I am trying to get grips with OpenFoam. I set up a really EASY case. It is some kind of straight tube. The simulation should be easy, but after 6 iterations, icoFoam diverges. I use the solver settings from the elbow testcase. Possible problems i thought on: mesh: it is really fine, much too fine (just to be sure) time step: is also set really small (dx=2/40 m, U=1m/s -> dt=0.05 should be sufficient, i set it to 0.01) boundary conditions: inlet with Velocity set to 1 m/s; p at outlet set to 0 Pa. The rest is wall. I checked BC several times, and i find no mistake I include the test case. the case is ready to blockMesh and icoFoam you will see, it diverges after 6 time steps. any hint is really appreciated! Roland |
I think my test case was not as simple as i thought. The geometry of the tube leads to secondary flows. however, i found out convergence with upwind divScheme is much better.
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I think the length of your tube in y direction is very small and you can not impose zeroGradient at the outlet I suggest you, to increase your length ten times of square root of section area |
mechy, thanks, although i checked the solver conditions several times i payed less attention on the geometry itself. It makes sense that the short tube interferes with the zeroGradient boundary condition. Thanks!
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is your problem solved with increasing length of tube ? |
yes, increasing the length solves the problem. Also i set the time step very low. maybe setting pressure boundary condition instead of velocity at inlet would also help convergence. but it works for me. thanks
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