Hi all, I am trying to solve a THM problem with staggered scheme using OGS6. I found that staggered scheme has been implemented into HT module but there is not any stablization concerning about the convective heat flux. Then I test a strong convective case with Eigen solver using the existing HT module in ogs6.4.4 and the results look good. But when I use my personal parellel computing branch to solve the same problem with petsc solver the simulation cannot get convergence

```
Linear solver cg with bjacobi preconditioner
Warning: maximum number of iterations reached.
[0] info: [time] Linear solver took 13.1202 s.
[0] info: Convergence criterion: |dx|=6.0949e+08, |x|=6.1496e+08, |dx|/|x|=9.9111e-01
[0] info: [time] Iteration #7 took 13.3224 s.
[0] info: [time] Assembly took 0.203315 s.
[0] info: [time] Applying Dirichlet BCs took 9.17912e-05 s.
Divergence detected, use command option -ksp_monitor or -log_summary to check the details.
[0] info: [time] Linear solver took 1.16567 s.
[0] error: Picard: The linear solver failed.
[0] info: [time] Solving process #0 took 95.6734 s in time step #1 coupling iteration #1
[0] warning: The nonlinear solver failed in time step #1 at t = 18 s for process #0.
[0] info: [time] Time step #1 took 96.9823 s.
[0] warning: Time step will be rejected due to nonlinear solver divergence.
[0] critical: /mnt/e/OGS-THMPF-REBASED/ogs/ProcessLib/TimeLoop.cpp:426 computeTimeStepping()
[0] error: The new step size of 18 is the same as that of the previous rejected time step.
Please re-run ogs with a proper adjustment in the numerical settings,
e.g those for time stepper, local or global non-linear solver.
[0] info: OGS terminated on 2023-12-07 20:08:24+0800.
[0] error: OGS terminated with error.
```

. I wonder if anyone can tell me what is the reason for such a good robustness of OGS in a strong heat convective problem. the attached .prj file for HT module is tested with both my personal and the master branch and I didn’t set any stablization methods like `FullUpwind`

and `IsotropicDiffusion`

.

By the way, though I set blocks of `Eigen solver computation`

for the linear sovler part in my project but my personal branch still used some petsc method like `Linear solver cg with bjacobi preconditioner`

to do the computation. Is this because I introduced Petsc so that all the projects will be solved in Petsc? Here is the link of my presonal branch:https://gitlab.opengeosys.org/yUHaOLiu-tj/ogs/-/tree/THMPF-REBASED/ProcessLib/THMPhaseField?ref_type=heads

Best,

Yuhao

2D-inj.zip (1.8 KB)