Learning Forum

[Weiqiang Liu]

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

[Weiqiang Liu]

I put the screen shot of mesh here

[Weiqiang Liu]

Hi all,

I tested dense mesh with much smaller aspect ratio and found non-ignition still happen. I think aspect ratio does not effect whether the mixture can be ignited. Besides, some boundary layer mesh aspect ratio is larger than that in my case in some applications. 

Best 

[wcao]

Hi Weiqiang,

The reason that the ignition does not happen can lie in many aspects. Since your temperature did increase to a high value, one possible reason for this might be that the flame is quenched due to high momentum in the inlet. Please double check the inlet flow rate. Besides, it is recommended to start the combustion modeling with a developed cold flow. 

If you are using steady solver, you can use a high temperature for the wall BC and set it back to normal when the combustion is stable. Thanks.

Best,

Weiyu

[Weiqiang Liu]

Hi Weiyu,

Thanks very much for your suggestions! I did read some paper in which the author just set the wall thermal boundary condition to a constant high temperature instead of convective or radiation heat transfer. This definitely can help with convergence.

Best,

Weiqiang