Learning Forum

[pascuan]

i am running the Chapter 14: Modeling Species Transport and Gaseous Combustion on steady and transient. However, when I at the results for mass fractions the results are not the same. Why is that?

References: steady on top transient on bottom for comparison

[RK]

Hello, nIn the transient case, it depends on the time step you are displaying the contour. n

[pascuan]

really? i ran it all the simulation all the way to 45 seconds from 1e-9 timesteps. There was no indication of combustion n

[Karthik Remella]

Do you have a converged steady state solution? Also, are you able to converge every single time-step in your transient simulations?nAre the two models exactly the same? nHave you tried running the simulation for a longer period of time? How long (of real time) do you think you need to simulate your problem needs before you can reach a steady state solution?nThanks.nKarthikn

[pascuan]

I do have a converged steady state solution. The solution is from Chapter 14: modeling species transport and gaseous combustion from the Fluent tutorials. nThe model used for the steady is used for transient, also,\ every time step in transient is converged. I have ran the simulation up to 45 secs but I really only need up to 1.3 since my ch4 species are in contact with my o2 species, however no combustion is happening(no mass fraction of h2o and co2 species on contours). My references are attached. First image is the steady state converged. 2nd image is the transient converged near flow time of 1.318 where contact between ch4 and o2 is seen. nThank you.nnn

[chz198515]

Hey, Did you find the solution to your query? I am doing the exact same study but with transient case. ? What is the reason for difference in results because of steady and transient cases ?

[SRP]

Hi,

The main difference between steady and transient cases lies in the consideration of time. The choice between these two approaches depends on the nature of the problem being studied and the level of accuracy required to capture the system's behavior effectively. For transient simulations, it's crucial to ensure that the chosen time step and simulation duration are appropriate to accurately capture the dynamic phenomena of interest. 

It also depend on the how you are initialize your problem. Transient simulation require better initial guess to achieve convergence.

Thank you.