Tagged: 16, convergence, Convergence Problems, fluent, fluid-dynamics, Species/Reactions
January 25, 2023 at 7:17 amFAQParticipant
The DASAC ODE solver is used for the direct integration of the chemistry. The messages regarding the DASAC failure suggests that the ODE solver (DASAC) failed to integrate the stiff ODEs, and that your solution is not converging well. If you see these messages during the initial few iterations, but notice them go away shortly after, there is no need to worry as the solver is trying to build your solution from the initial conditions specified. However, if you continuously see these messages even after running the solution for a sufficiently large number of iterations, then it means something is wrong with the setup/initial conditions. Most of the time, we can get rid of these messages by specifying a good initial solution (e.g., solution obtained from Finite Rate/Eddy Dissipation model using global reactions). You can also check the material properties, especially the specific heat polynomial coefficients. Use of correct properties will help to avoid these failures. Lastly, your reaction mechanism will also affect the DASAC integration. Please check if the reaction mechanism is correct. If you are using a CHEMKIN import, please make sure that the units mentioned in the CHEMKIN file is correct.
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