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-   -   Static temperature remains constant in a combustion simulation (https://www.cfd-online.com/Forums/fluent/237870-static-temperature-remains-constant-combustion-simulation.html)

Khadorna August 10, 2021 04:10

Static temperature remains constant in a combustion simulation
 
Hi, i've been trying to get a combustion simulation of a hydrogen/methane mixture working by using the reduced GRIMECH 3.0 kinetics and transport given by fluent. The transport properties seem to work correctly as the contours for the system show expected results.

I need to get a contour of the static temperature, but it only varies in like 0,5K and i don't really know why as im trying to simulate combustion. With the individual components and a simpler mechanism, it works just fine.
Should I deactivate the tracking of the reaction intermediates? Is something wrong with the thermo file?

Thank you in advance

LoGaL August 10, 2021 18:37

So the species distribution is reasonable but the temperature is not? Is it cold everywhere as if there was no flame?

Khadorna August 11, 2021 03:07

Quote:

Originally Posted by LoGaL (Post 810055)
So the species distribution is reasonable but the temperature is not? Is it cold everywhere as if there was no flame?

Exactly. The species distribute accordingly I think, but temperature (set at 300K) does not increase anywhere in the system.

I've tried to reduce step time, increase the number of iterations, but that point converges and Fluent does not get anywhere else.

LoGaL August 11, 2021 05:40

Usually you need some manner to kickstart the combustion, a sort of numerical spark if you want.

So basically, you should patch (i.e. impose) the combustion chamber region with a high temperature (1800K) once the cold flow is properly developed, as in your case. Just google “fluent patch region” and you should find plenty of instructions on what to do

Khadorna August 12, 2021 04:51

Quote:

Originally Posted by LoGaL (Post 810088)
Usually you need some manner to kickstart the combustion, a sort of numerical spark if you want.

So basically, you should patch (i.e. impose) the combustion chamber region with a high temperature (1800K) once the cold flow is properly developed, as in your case. Just google “fluent patch region” and you should find plenty of instructions on what to do

I've tried patching a small region of the combustion chamber with a high temperature, kind of emulating a spark as you said, but the result did not change at all. Should i patch a bigger region of the combustion chamber? (maybe like half of it?) or should it work with what I set up?

Thank you for your help

LoGaL August 12, 2021 05:45

I usually patched the whole combustion chamber ;). If you see it diverges, either underelax a bit the equations for 20-30 iterations or, if you are using pseudo transient method, set a lower multiplicator


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