LES Combustion Boundary Condition
 

hi all,

I am currently developing an LES model for combustion using the flamelet/non-premixed combustion model but I am having a problem...

I calculate the correct air and fuel inlet boundary conditions (I have tried both velocity inlet and mass-flow inlet), and I know they are correct as when I run them with the k-epsilon model it gives the correct overall mixture fraction and peak flame temperature, etc.

But then when I run it with LES for a while (1-2 flow throughs) the fuel concentration becomes too low and the time-averaged mixture fraction becomes lower than that initially calculated or predicted by the RANS run.

I then need to increase the fuel flow until the model gives the correct overall average mixture fraction or equivalence ratio (at the outlet).

Has anyone else encountered this issue?

Thanks

can anyone share any insight? even the smallest clue could help a lot...