Learning Forum

[Shin]

Hello ANSYS Support,

I am encountering some issues during my simulation and need your assistance, as I couldn’t find similar problems or solutions online. At the beginning of my simulation, the time step is 1.0e-5. However, as the simulation progresses and H2 injection into the intake begins, the time step gradually decreases to 1.0e-12. After running for a while, the simulation stops automatically with an error indicating excessive recycling and a very small time step.

I have attempted to adjust the time step, but the same error persists. Could you please provide me with some advice? Thank you.

[jcooper]

Hi Shin:

H2 Chemistry is very stiff. The reaction zone for h2 is much thinner than for other fuels, so the mesh and timestep requirements are stricter. You could try the same simulation with 1 deg per timestep, but this will not be enough if the mesh is too coarse. 

Another thing to check is your refinements.  Things often start to go wrong long before the solver fails. If you know when the simulation will fail, run it again and set it to stop just before the failure.  Post process the solution for clues on where the mesh may be insufficient to resolve temperature and species gradients.

Best Regards,

Judy