The issue of time step on simulation of viscoelastic fluid's upstream flow at high Wi
 

Dear all, I am now adopting rheoTool(A open tool at framework of openfoam) to simulate the viscoelastic fluid's upstream flow at high Wi. The algorithm is implanted based on this manuscript:https://arxiv.org/ftp/arxiv/papers/2203/2203.09239.pdf
When the case's time step is set to 0.001s, some upstream flow is observed. However, the case would be collapsed as continue to run it. Then the starting time step is set to 0.0001s. The case would be run all the time. However, the case always presents steady feature where the upstream flow would not be observed.
The case and solver is uploaded. All suggeations are welcomed. Thanks a lot.