Fluids

Fluids

Floating Point Error in FGM combustion transient

    • pester98
      Subscriber

      Hi, 

      I am currently performing a reacting case of a swirling combustor. My model is (partially premixed combustion) FGM diffusion model. I ran an initial steady case, and it worked perfectly fine converging well, and when comparing velocity profiles versus experiment, they were really good. I am now trying to do the same case but transient, to do this, I used my steady state solution and ran the transient case with a time step of 1e-6 to keep the courant number well below 1. The turbulence model used in k-e realizable. When running the transient case at the first time step, the solution diverges, and a floating point error is given. I am using a coupled solver with a very low URF, but I still have the same issue. I tried using SIMPLEC as well but still same error. I also tried to patch the progress variable to 1 and still diverged, and then tried to patch it to 0 and still diverged. Any ideas about what could be the issue and how to sort it out?

      Thank you,

      Nick 

    • Rob
      Ansys Employee

      I'm not aware of anything that'll cause that in the FGM model, I also asked one of the European experts. Have you got any expressions, profiles or UDFs attached to the case?

    • pester98
      Subscriber

      Hi Rob, 

      Nothing attached. Just the mechanism file and thermodynamics at the beginning to create the PDF table for the FGM. Are there any good practices you recommend when doing combustion transient (setup, timestep, etc.)?

    • Rob
      Ansys Employee

      If it worked steady we're not sure why transient isn't working. Please can you add screen shots of the species & combustion panels. 

    • pester98
      Subscriber

      Hi Rob, 

      Please find below the images. 

      Thank you,

      Nick 

    • Rob
      Ansys Employee

      That looks fine. Which version of Fluent are you using?

    • pester98
      Subscriber
      2021 R1
    • Rob
      Ansys Employee

      Some comments from over the weekend. A couple of colleagues have seen an error but it's not repeatable enough to diagnose. 

      Try restarting after switching to transient, ie switch over, write case & data. Close Fluent. Open Fluent & load files. 

      Double check you have got the time step set correctly. There's a GUI glitch which can void the setting, check the ribbon AND tree menus are seeing the same result. 

    • pester98
      Subscriber

      Will try that. Thank you very much for your time and help, Rob. 

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