A novel method to apply artificial neural network (ANN) for both chemical kinetics reduction and source term evaluation is introduced and tested in direct numerical simulation (DNS) and large eddy simulation (LES) of reactive flows. To gather turbulence affected flame data for ANN training, a new computation-economical method, called 1D pseudo-velocity disturbed flame (PVDF), is developed and used to generate thermo-chemical states independent of the modeled flame. Then a back-propagation ANN is trained using scaled conjugate gradient algorithm to memorize the sample states with reduced orders. The new method is employed in DNS and LES modeling of H2 /air and C3H8 /air premixed flames experiencing various levels of turbulence. The test result shows that compared to traditional computation with full mechanism and direct integration, this method can obtain quite large speed-ups with adequate prediction accuracy.
A finite reaction rate model is presented as a closure of large eddy simulation(LES) to numerically study an open premixed methane/air swirling flame. The resultant model is firstly validated by comparing with reported data and then employed to investigate the effect of swirling intensity on flow field, flame characteristics and combustion instability of the swirling flame. Three different swirl numbers are considered. The LES results show that as swirling intensity increases, the vortex entrainment and micro-mixing are enhanced, leading to more lean equivalent ratios at flame front; consequently, higher swirling number causes lower flame temperatures and slower CO oxidization; for all simulated swirl numbers,flame fronts are completely located out of the recirculation zones and anchored at the inner surface of the annular swirling steams; swirl number has a crucial effect on swirling flame extension toward radial and tangential dimensions and then significantly affects streamwise flame length, which is a great influencing factor on combustion instability; vortex-induced disturbance on flame in streamwise plays a critical role in combustion instability.
