{"id":370986,"date":"2024-07-08T15:59:44","date_gmt":"2024-07-08T15:59:44","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/forum\/forums\/reply\/370986\/"},"modified":"2024-07-08T15:59:44","modified_gmt":"2024-07-08T15:59:44","slug":"370986","status":"publish","type":"reply","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/reply\/370986\/","title":{"rendered":"Reply To: Multiphase VOF simulation of a rotating capillary tube"},"content":{"rendered":"

<p>I am replying late as the forum was down for maintenance a long time. I downloaded 24R1 and tried running the same case, but that didn’t lead to substantial changes. The timestep sizes that were diverging before are still diverging, even if a little later with actually slightly different contours, the stable ones from before lead to basically identical results.<\/p><p>Timestep 3e-5s, Velocity limited to 50m\/s, Wall rotating at 1 rad\/s<\/p><p><\/p><p>Timestep 1e-5s, Velocity limited to 50m\/s, Wall rotating at 1 rad\/s<\/p><p><\/p><p> <\/p><p>As the densities of the two phases are very different and hence the problem that arose was excactly what Fluent describes as critical for stability, I tried pushing the velocity limiting even further (to 1m\/s, with 3e-5s as timestep), as 1rad\/s with a radius of 1mm means speeds in the orders of magnitude around 0.01m\/s. Unfortunately this lead to unphysical results, something known in the Fluent Guides. It’s also worth noting that I cannot replicate this unphysical contour (which is present throughout the whole calculation) using smaller timesteps (they would again lead to a fully “flat surface”, looking exactly as if there was no rotation imposed at all). <\/p><p><\/p><p>Increasing the rotational speeds to 50rad\/s constant or applying a 50rad\/s triangular peak don’t change the profile when simulating with the timestep size 1e-5s, and with bigger timesteps I get the same divergence as before. The backflow in on the open boundary changes a little, indicating to me that Fluent is not disregarding the change in rotational speed; but as to what I expect from the solution and want to prove I am not able to get the software to perform results that should be phyiscal in my opinion.<\/p><p>Timestep 1e-5s, Velocity limited to 50m\/s, Wall rotating at 50 rad\/s<\/p><p><\/p><p> <\/p><p>I’d be glad about final thoughts on where these problems could arise from and what I could be doing wrong.<\/p><\/p>\n","protected":false},"template":"","class_list":["post-370986","reply","type-reply","status-publish","hentry"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t