Fluids

Fluids

Stable temperautre changes after reloading and restarting

    • Moritz
      Subscriber

      Hi guys,

      I am currently simulating biomass gasification in an entrained flow reactor. Even though all my residuals (energy, velocities, species,..) are reasonable converged and also the different parameters (molar fractions of species, velocities, wall fluxes, temperature,..) displayed in my report plots are stable, I get a new stable temperature niveau at the outlet after reloading and restarting my simulation (same case and data file), which is often up to 60 K lower/higher. 

      Any suggestions why this is happening or how to get the same results after the restart ?

      Thank you in advance,

      Moritz

    • Rob
      Ansys Employee

      Fluent shouldn't do that. Please can you post the report monitors so I can see how they behave on restart, residual too.  Have you got any expressions/profiles/UDFs hooked up that need/calculate data in the background? With poor meshes I have seen jumps in values for very stiff problems as the gradients aren't retained in the data file: the restart recalculated the gradients with very slightly different values which then altered the solution. Both results were numerically correct and revising the mesh to better capture the gradients fixed this. 

    • Moritz
      Subscriber

      Thank you for the quick response. I have a UDF hooked calculating particle reaction rates.

      The other monitors are either the same or change according to the change in temperature. 

    • Rob
      Ansys Employee

      In which case it's possibly the UDF recalculating based on cell values on restart. Check the flow gradients and DPM source terms, you may need to increase the parcel count and/or refine the mesh to capture all of the gradients.

      However, if the average is jumping around as per the second graph I suspect it's either unstable or slightly transient which won't help. 

    • Moritz
      Subscriber

      Okay I am going to check these. Thank you for helping.

Viewing 4 reply threads
  • You must be logged in to reply to this topic.