October 5, 2022 at 12:27 pmfriday.abolorunkeSubscriber
I am simulating a two-phase multicompoent flow with a porous and open region.
VOF model, Species transport, Laminar flow. UDF for interfacial mass transfer.
Average mesh quaility: 0.99998, sqewness 0.0105. I dont think the issue is with the mesh. Also, the UDF is fine. I have used it to solve another problem without porous media and this float point issue did not occur. No dynamic mesh.
The simulation suddenly diverges after running for a flow time of about 11s. Even though the solution converges each time step before suddenly diverging.
I think the issue is from the liquid-species. Please has anyone encountered this before? what can I do? See picture attached.
October 5, 2022 at 1:28 pmRobAnsys Employee
How does the flow look a bit before divergence? Ie has a free surface position suddenly shifted, or mass transfer altered.
October 5, 2022 at 1:36 pmfriday.abolorunkeSubscriber
The condition for the mass transfer to begin has not been met, so the interfacial mass transfer is zero. I don't think there is a change in the flow field. I am running the simulation in batch mode without saving contour plots or data files during the simulation.
October 5, 2022 at 1:43 pmRobAnsys Employee
No data saves? What are you going to post process? How has the time step altered over the last 10-50 time steps? Back flow may trigger problems, but it can also be an indicator that something else is going on.
October 5, 2022 at 1:58 pmfriday.abolorunkeSubscriber
The time step size did change much for the last 50 time steps. Between 1.3755e-3 - 1.44e-3. The max time step is 35 and the simulation consistently converges around 10th - 8th time step.
I did not save the data file because I have a different model that runs without issues, except it has significant reverse flow that leads to mass loss at the inlet. I made some changes to the shape of the inlet to try to eliminate of reduce reverse flow.
October 5, 2022 at 2:26 pmRobAnsys Employee
OK. Unfortunately you'll need to re-run to about 10.5s and then save more data from there. Adaptive time stepping can trigger instabilities if the oscillation interacts badly with the flow time scales.
October 5, 2022 at 2:34 pmfriday.abolorunkeSubscriber
I will do that and let you know what the flow field looks like. Thank you.
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