Strange result when creating animation

Description: My project simulate H2 flow in a pipeline

  1. After the simulation, the result looks very strange (Youtube). I expected gas velocity increasing from left (inlet) to right (outlet) and pressure decrease from left to right. Here there is a long inactive process and then suddenly the pressure increases. What is wrong with my simulation

  2. The animation shows only pressure, but can I get the velocity from the solution field too?

Link to project:

Hey there!

I think your simulation has not achieved numerical convergence. I can tell by having a look at the convergence plots:

If the simulation has not converged, then your results are not valid. Also, you are animating the values against the iterations, which can me misleading because all intermediate values are not valid, just the converged ones. Typically only the last one is analysed.

In order to get converged results, you can:

  • Run the simulation for more iterations. I suggest try 3000 iterations.
  • Refine the mesh.

This article should also help:

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Thank you for your link, I set end time as 3000s with write interval 10, which I guess coresponds to 3000 iterations

If I download the solution field, there is a .foam files and a bunch of numbered folders which I guess respond to iteration? Are you suggesting look at only the highest numbered folder?

Later I would like to do a spatial and time analysis. Would it be possible when only looking at the last iteration?


Yes, in this case for steady state simulation, the ‘end time’ corresponds to the number of iterations. It is not really physical time.

The write interval of 10 is only writing additional, non-converged and thus invalid results to the output, making it unnecessarily bigger. We always write only the last iteration, e.g. for your case write interval should be 3000.

You can not make a time analysis with a steady state simulation, for that you would need a transient analysis, where actual time is taken into account.