Fluids

Fluids

Divergence in solution despite decrease in residuals

    • 164170007
      Subscriber

      Hello all, I am doing simulation of catalytic reaction of hydrogen with air in presence of catalyst, where I have many inlets (BLUE LINES). 4 small inlet for hydrogen and 1 inlet for oxygen and 1 outlet and whole reactor is coated with catalyst (neglecting small dimensions of hydrogen inlet geometry).

      I am using UDF for kinetics which is giving correct result with literature when hydrogen and air are enetring with one inlet (No multiple inlets), so I dont think its because of UDF. But in the multiple inlet geometry I only changed the boundary conditions of species mole fraction which I gave 1 for H2 and 1 for O2 for multiple inlet case. (ONE INLET CASE I had given H2/O2 ratio like 0.5:0.5 at the inlet). The whole simulation is for steady state and laminar conditions and I am using species transport volumetric reactions model for both cases.

      I am not getting what wrong is happening with simulation and why despite decrease in residuals its showing divergence error. Please see the mesh for my simulation, I dont think its an issue. 

      Thanks in advance,

      Regards,

      Vinay

    • Rob
      Ansys Employee

      If you plot the results at 1000, 1500 and 2000 iterations how does the model look? I'm wondering what's causing the instability, and the earlier results may give some clues as to what's going on. 

    • 164170007
      Subscriber

      Hello Rob,

      I plotted the temperature contours and plot for 5000,10000,15000 iterations and after 15000 iterations its getting diverge. ( I reduced the relaxation factor in comparision with previous results). Please see the attached figure and let me know what mistake I am doing

       

    • Rob
      Ansys Employee

      I don't think you're doing anything wrong as such. The first hydrogen inlet triggers a reaction with the oxygen supply. That gives a very high temperature reason, and may or may not use up a large amount of oxygen. You then get an unstable flame in the system.  Without knowing what the other settings (inlet, material density etc) I can't really guess what's going on, but suspect the model is OK, but possibly missing something when compared to reality. 

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