Problem on simulating (polimi) soot model

4 years 1 month ago #42 by Hafiz
Quick update: I increased endTime and it seems to be fine (still running). The temperature rose to 4100 K though. Just want to check if things are in order. This is the latest log file:

File Attachment:

File Name: logupdate.txt
File Size:19 KB

PS: apparently the log file is now around 100+MiB so I cant attach the full log. (I'm assuming things are going well)

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4 years 4 weeks ago - 4 years 4 weeks ago #43 by Hafiz
I had to changed my system because it was too slow and I was basically running on two cores.. so now I've updated a new system with 32 cores (Intel Xeon) and could see improvements in simulation time. Right now, I have finished running the test cases on GRI model and moving onto bigger species. However, I've noticed that deltat goes very small (upto e-17) and so simulation still goes very slow. I've just changed runTimeModifiable and adjustTimeStep to "no" and decrease my deltat and hopefully see any changes (temperature rose to 5000 K >).

Anyway, is there a reason why deltat goes very very small and how could I tackle this problem correctly? (I only see this problem when I changed the reaction kinetics model)
Last edit: 4 years 4 weeks ago by Hafiz.

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3 years 9 months ago #50 by acuoci
From your log file it is evident that the local ODE solver is not able to solve correctly the chemistry. A possible explanation is related to the different names of species when you move from the GRI mech to the POLIMI mech. Let me better explain this point. The POLIMI mechanism is larger tha the GRI, so in principle you expect that all the species available in the GRI are also present in the POLIMI. This is reasonable to imagine, but not necessarily true. Moreover, the same species can have different names in the 2 mechanisms. In both cases (a species in GRI in not present in POLIMI and/or different names) there is a numerical problem: when you move the solution from GRI to POLIMI you loose the mass associated with the missing species. If the mass loss is relatively small. laminarSMOKE can manage, by replacing the missed mass with nitrogen. However, if the lost amount is large, numerical issues arise. Thus, the first option is to check if this is the case, i.e. if there are no issues in transferring the solution from GRI to POLIMI and to be sure that the same species have the same names.
A second option, which is convenient to use more in general when you change the kinetic mechanism, is the follwoing: instead of start solving the whole system of equations (momentum, temperature and species), it is better to proceed gradually, by freezing first the momentum and the temperature equation (i.e solving only for species), then enabling the temperature, and then the momentum too.
The following user(s) said Thank You: Dong-Sheng

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