# VOF tank filling/emptying - divergence during emptying

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• Last Post 11 November 2019
• Topic Is Solved
desouzadacosta posted this 07 November 2019

Hi All

I am trying to simulate a tank filling from the bottom, valve opening and emptying .

The filling is going fine, but after the opening of the valve, the emptying operation is showing divergence in the k field :

Global Courant Number [Variable Time Step Criteria] : 7.135128
Updating solution at time levels N and N-1.
done.
physical-dt  1.0000e-05

iter  continuity  x-velocity  y-velocity  z-velocity           k       omega    vf-water     time/iter

reversed flow in 259 faces on pressure-outlet 14.

reversed flow in 259 faces on pressure-outlet 14.

reversed flow in 259 faces on pressure-outlet 14.

reversed flow in 259 faces on pressure-outlet 14.
Stabilizing k to enhance linear solver robustness.

Error: Divergence detected in AMG solver: k

Error: Divergence detected in AMG solver: k
Error Object: #f.

I already tried the turbulence damping, k-epsilon, k-omega, implicit/explicit VOF, reduced time step, options without success.

I reproduce below some pictures of the simulation. Any expert advice is very welcome.

abenhadj posted this 07 November 2019

How is the opening of the valve modeled? Switching boundary condition? When dies divergence occur?

Best regards, Amine

desouzadacosta posted this 07 November 2019

Thanks for the reply. It is changed from wall to interior using execute commands, after some volume of water is reached.

abenhadj posted this 08 November 2019

And when does it diverge?

Best regards, Amine

desouzadacosta posted this 08 November 2019

At t = 3.672 s

abenhadj posted this 09 November 2019

Ok. What is the boundary condition applied in the bottom? Try with Tait equation for water.

Best regards, Amine

desouzadacosta posted this 10 November 2019

Sorry. How to use Tait equation?

abenhadj posted this 11 November 2019

Compressible liquid.

Best regards, Amine