Learning Forum

[TingWangUNO]

Hello,

I recently ran a simulation trying to move a rib in a 2D approximation of a cylinder using the dynamic mesh motion. The flow is modelled as a two phase flow using the Eulerian multiphase model. The case is also run as transient. The mesh around the rib is shown below.

The preview of the mesh motion showed the rib moving smoothly and without issue. The dynamic mesh zone was set to rotate with an angular velocity of 16.5 rad/s. With a radius of 1.45 m, the maximum tangential speed experienced should be 23.9 m/s. However, in the region near the rib, the velocity of the water shot up to almost 3500 m/s. The maximum facet velocity and the contour of velocity magnitude in this region (both for the water phase) are shown below.

The mesh motion is described using a UDF, with a constant angular velocity of 16.5 rad/s, defined using CG_MOTION. The UDF written is:

 

I'm currently trying to troubleshoot what could have caused this issue. I can provide more details if they are needed. As I go through the troubleshooting process, I'm curious if there is anything that stands out as an immediate culprit.  

Thank you. 

[Federico Alzamora Previtali]

What is your timestep size here? It looks like your inflations layers are really fine, which may require to reduce your timestep.

Maybe plot CFL contours near the rib and confirm that it is not exceedingly large.