Learning Forum

[Weiqiang Liu]

Hi all,

I posted a thread about methane combustion simulation before, in which I encountered convergence issue. 

Then I tried to use stiff chemistry solver in stead of the default non explicit source in species transport setting panel. Then my results are very close to literature value. 

I am wondering what's the difference of stiff chemistry solver and non explicit source option.

If stiff chemistry solver can better solve combustion problem, why fluent does not use stiff chemistry solver as default? What is the disadvantages of stiff chemistry solver?

Best regards

Weiqiang 

[Rahul Kumar]

Hello, 

Some of the reaction mechanisms have high kinetic rates, in general, flows characterized by Da >> 1, where the reaction times are much faster than the rates of diffusion and convection. In this case, the system becomes stiff. When the stiff chemistry is enabled, it provides solution stability to the solver by limiting the local CFL number when the temperature changes rapidly. 

For a more information, please refer to the Fluent user's guide: 

https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v201/en/flu_ug/flu_ug_sec_species_mag_soln.html

[Weiqiang Liu]

Hi Rahul,

Thanks very much for your reply. It's very helpful!

Weiqiang