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maximum aspect ratio of mesh

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Old   June 3, 2020, 09:46
Default maximum aspect ratio of mesh
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Hi all,

I am doing a methane combustion simulation with fluent. I followed the node distribution in literature and drew the same mesh with the author.

Because the geometry is a very thin channel, the final mesh has very large aspect ratio with maximum aspect ratio 150.

I used this mesh to continue my simulation. Divergence did not happen with this mesh. However, I can not ignite the mixture like the author did. Temperature would increase to a high temperature and then drop to room temperature.

I am wondering could this mesh with high aspect ratio be the reason why I can not ignite the mixture? will large aspect ratio mesh effect results accuracy?

Can somebody who has combustion simulation experience give me some suggestions?

Best regards

Weiqiang
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Old   June 3, 2020, 09:50
Default Aspect Ratio
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The effect that you observed cannot be because of mesh. AR 150 is an order of magnitude smaller than what is used in boundary layers for high speed flows. So, this will not affect the physics they way your are observing. Either there is some heat loss or the parameters given for the reaction kinetics (provided you are using finite rates) are incorrect. Check material properties as well.
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Old   June 3, 2020, 09:59
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Quote:
Originally Posted by vinerm View Post
The effect that you observed cannot be because of mesh. AR 150 is an order of magnitude smaller than what is used in boundary layers for high speed flows. So, this will not affect the physics they way your are observing. Either there is some heat loss or the parameters given for the reaction kinetics (provided you are using finite rates) are incorrect. Check material properties as well.
Hi,Vinerm

All chemical kinetics, thermal and transport are imported into fluent with CHEMKIN files.
Actually my gas phase mechanism is different with the author's. Mine is simpler due to the limitation of computation power. I tried to keep other settings the same with the author. Do you think will the difference of gas mechanism cause ignition failure?

Thank you

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Old   June 3, 2020, 10:02
Default Mechanism Reduction
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If it is a reduced mechanism then it has to be done carefully. Chemical mechanism reduction is a field of study in itself. I'd suggest you to try with elemental reactions before using detailed kinetics.
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Old   June 3, 2020, 10:04
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Quote:
Originally Posted by vinerm View Post
If it is a reduced mechanism then it has to be done carefully. Chemical mechanism reduction is a field of study in itself. I'd suggest you to try with elemental reactions before using detailed kinetics.
it's simpler mechanism which is also used by other authors. Thanks very much for your suggestions

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