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July 2, 2020, 12:02 |
time step of twophaseeulerfoam
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#1 |
Senior Member
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Hi guys,
I am using twophaseeulerfoam to simulate the solid-liquid pipe flow. The total number of the cells are 180000 (unstructure mesh) but I need to set a very very small time step to keep simulation normally runnning. Do you have any suggestion that I can define a larger time step? I saw some people used this solver to simulate the same phonomenon. They used more cells than mine. I cannot imagine how much time they used to finish one simulation if the situation like mine. Thanks, |
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July 2, 2020, 14:40 |
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#2 | |
Senior Member
Ruben Di Battista
Join Date: May 2013
Location: Paris
Posts: 137
Rep Power: 13 |
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July 2, 2020, 20:47 |
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#3 | |
Member
Ardalan
Join Date: Jul 2012
Location: Atlanta, USA
Posts: 77
Rep Power: 14 |
Quote:
If you do not need energy equation discard it in the solver. If you need it specify correct boundary conditions in T files. diameterModel in phaseProperties matters as well. If comprisibility matters to you a lot, e.g.sonic jet or so on, It will be reflected in p_rgh, therefore it wont be a sudden crash. Anyhow, small courant number in the order of 0.1 may help too. Good luck Ardalan |
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July 3, 2020, 03:15 |
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#4 | |
Senior Member
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Thanks a lot. As you said, I already neglected energy euqation. Even though I set maxCo 0.1, the maximum time step is 2e-5 or 2e-6. The totall cells are 260000. How about your time step used in the simulation?
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July 3, 2020, 03:24 |
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#5 | |
Senior Member
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Thank you. I uploaded my test files and mesh here. Could you please help me to have a look? By the way, the parameters in slurry pipe I used are the following:
pipe diameter 0.1 m (only half) particle diameter 1e-4 m Uin=2.5 m/s alphas=0.2 Quote:
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July 3, 2020, 03:29 |
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#6 |
Senior Member
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I uploaded the files here without mesh, due to the large size.
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July 3, 2020, 03:38 |
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#7 | |
Senior Member
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I saw your previous post and I checked your test case uploaded there. The timestep in your case is 2e-4 s. So you need several days or more to finish one simulation?
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July 6, 2020, 10:30 |
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#8 |
Senior Member
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Nobody is curious about this issue?
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July 6, 2020, 11:38 |
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#9 | |
Senior Member
Ruben Di Battista
Join Date: May 2013
Location: Paris
Posts: 137
Rep Power: 13 |
Quote:
actually.. no. Running the test case in parallel the test would finish in a matter of hours... Why do you say days? Are you running in parallel? |
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July 7, 2020, 08:27 |
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#10 |
Senior Member
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Thanks. I did not try parallel but in the end I will do it. I am curious that there is the way to increase the time step.
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July 7, 2020, 08:32 |
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#11 |
Senior Member
Ruben Di Battista
Join Date: May 2013
Location: Paris
Posts: 137
Rep Power: 13 |
With a very basic explanation: The time step of a simulation can't be arbitrarily changed. Based on the time and space schemes you are using, there's a so-called CFL condition that restricts the maximum time step you can achieve. This CFL condition takes also in consideration the cell size: that means if you have a very fine mesh, you're generally gonna have a small time step to keep the numerical scheme stable.
What you can do to increase the time step is to compromise on some aspects: - Use a coarse mesh - Use low order numerical schemes that have larger stability regions - Use implicit time schemes - Increase the Courant number (that will reduce your stability) |
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July 7, 2020, 08:42 |
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#12 |
Senior Member
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Hi guys, I met a new problem that the converency issue between the unstrcture mesh created by workbench and structure mesh generated by blockMesh. Why the iteration of P_rg is 1000, which means unconverged, right? Do you habe any suggestion? Thank u.
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July 7, 2020, 08:52 |
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#13 | |
Senior Member
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Thanks a lot. I already considered what you mentioned below however, the time step is the samll one. Now I regard that issue as normal one. Really thank u. Gentilissimo!
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timestep, twophaseeulerfoam |
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