Learning Forum

[Vipul Gupta]

I am working on VOF multiphase simulation. Everything was ok up to 138 seconds, but suddenly after 138.18 seconds, the correct number increased to a high value of more than 250. Velocity unexpectedly becomes very high. Maximum velocity reaches 220124 m/s. The simulation stops with a floating point exception error. 

How to resolve this issue 

[Rob]

I assume you mean Courant Number. 

What happens in the flow at around that time? Ie does something change? If you restart from an autosave case & data does the error repeat?

[Vipul Gupta]

I mean Golbal courant number. I used the adaptive time step method for time step size. Velocity becomes very high around this time. I restarted from an autosave case and data. The issue remains the same. 

[Rob]

Turn off adaptive time stepping and see what's going on. The function can be very useful for flows with gradual changes in time scale, if something suddenly changes the scheme may not drop the time step rapidly enough. 

[Vipul Gupta]

Please check the below attachments (volume fraction, velocity vectors). These are at 138 seconds. 

 

 

[Vipul Gupta]

Right side middle plane velocity vectors plot goes to near 155 m/s which is unrealistic. 

[Rob]

That's the traditional "big red vector". Check the mesh in that region and that you're resolving the gas phase as it looks like a very narrow gap between the wall & free surface.