[Eleven Leo]

Hi,

In Converge manual, It is said "In SAGE mode, a flame front that is well solved through AMR." Do it means that the complicated curve of flame front can be well described with more refined mesh? Moreover, I want to know how to distinguish the flame propagation and auto-ignition.

Thank you very much for your help.

Best.

[SamWijey]

Hello,

AMR does help in resolving the turbulent flame thickness. However it is important we understand that this 'resolved thickness' can be different from the actual turbulent flame thickness. Numerical viscosity from Low order numerical schemes, larger cell sizes, and the turbulence model can artificially thicken the flame. Hence in a RANS simulation, we can never resolve Kolmogorov length scales because these small scales are non-existing.

Using AMR, we can resolve the available "RANS lengthscales" which are typically in the order of 1-0.1 mm for IC Engine cases.

LES simulations, can approach DNS in the limit of sufficient mesh resolution. However, resolving laminar flame thicknesses (which are in the order of 1-10 microns) in engineering combustion systems (ICEs, GTs,etc..) is quite expensive even with today's computational resources.

So when CONVERGE manual says "In SAGE mode, a flame front that is well solved through AMR" what it means is that AMR can be used to efficiently resolve the turbulent flame front with all its wrinkling. Again this resolved flame surface area can be different from the actual flame surface area due to artificial numerical thickening.

Thanks,

[Eleven Leo]

Originally Posted by SamWijey

Hello,

AMR does help in resolving the turbulent flame thickness. However it is important we understand that this 'resolved thickness' can be different from the actual turbulent flame thickness. Numerical viscosity from Low order numerical schemes, larger cell sizes, and the turbulence model can artificially thicken the flame. Hence in a RANS simulation, we can never resolve Kolmogorov length scales because these small scales are non-existing.

Using AMR, we can resolve the available "RANS lengthscales" which are typically in the order of 1-0.1 mm for IC Engine cases.

LES simulations, can approach DNS in the limit of sufficient mesh resolution. However, resolving laminar flame thicknesses (which are in the order of 1-10 microns) in engineering combustion systems (ICEs, GTs,etc..) is quite expensive even with today's computational resources.

So when CONVERGE manual says "In SAGE mode, a flame front that is well solved through AMR" what it means is that AMR can be used to efficiently resolve the turbulent flame front with all its wrinkling. Again this resolved flame surface area can be different from the actual flame surface area due to artificial numerical thickening.

Thanks,

Hi Sameera,

Thank you very much for your detailed answer.

Best.