[Tanjina]

Hello everyone,

Hope everyone is doing fine. I am modeling a 3D model of underdrain pipe flow. I am using parallel computing. Details about the model is :

Inlet: pressure inlet with hydrostatic pressure
outlet: pressure outlet
wall and symmetry

Solver: Pressure based
Model: Standard k-e model
Solution Method: coupled
Least square cell based gradient and 2nd order upwind momentum

Time : transient

URF was all 1 except k and e. Those were 0.8

I started with 0.0015 time step. After running 5 second ( almost 35000 iteration) it gave the error " divergence detected in AMG solver: k"

so I reduced all URF to 0.7 . Then it gave the error " divergence detected in AMG solver: epsilon ". I reduced the URF to 0.5~0.6. Then it gave several error after 2.7 sec run time.

# Divergence detected in AMG solver: pressure coupled --> Decreasing coarsening group size!
# Divergence detected in AMG solver: pressure coupled --> Increasing relaxation sweeps!
# Divergence detected in AMG solver: pressure coupled --> Changing to W-cycle!

turbulent viscosity limited to viscosity ratio of 10^5 in 93000 cells.

Please find the following image for error and residuals. I tried with Flow courant number 100, but no improvement.

Before showing error it gives same mass flow rate in outlet for long time, which I assume as converged.

I am not an expert in CFD field. Trying to learn these things for my thesis. Hope someone can help me how can I get rid of these error. Thanks in advance

Regards,
Tanjina