time step of twophaseeulerfoam
 

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,

Hello qi.yang, I think you might get more helpful comments if you give more details about your configuration. You can check my old post for an example of which details might be interesting. :)

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

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?

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

I uploaded the files here without mesh, due to the large size.

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?

Nobody is curious about this issue?

Hello,


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?

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.

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)

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.

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!