why the flame shape is quadrate?
 

Hello, everybody

I am simulating premixed flame propagation in channel using FLUNET based on density-based explicit solver. The mixture is ignited at one end, and then propagate to another end.

The flame propagation is described using progress variable. The turbulence model is LES. I use the uniform structured hexahedral grid. My problem is that at the initial stage in the simulation the flame shape is always square/quadrate , not spherical. It seems the flame takes the shape of the grid. However, in the experiment, the flame shape is spherical at the initial stage.

I tried everything I can to avoid this problem, but I failed. This problem is driving me crazy. Could any one help me? Thanks very much in advance!

Fireman.