Three-dimensional numerical simulations on spherical expanding flame of premixed natural gas/air mixtures.

• 3D LES simulation is conducted on spherical expanding flame of premixed natural gas/air mixture. • 3D flame front is decomposed into 36 2D flame fronts by rotation of the ZOX cross-section. • Flame morphology, flame propagation speed, cellular instability and disturbance are analyzed. • Disturbance amplitude and wave number of the flame perturbation are extracted by FFT. • Effects of spark energy, spark radius and time step on the simulation results are discussed. The flame dynamic and cellular instability of spherically expanding flame for premixed natural gas/air mixture were studied by numerically solve the 3D, transient, reactive Navier-Stokes equations. The computational methodology uses large eddy simulation and premixed combustion model with adaptive mesh refinement. The 3D flame front is decomposed into 36 2D flame fronts by every 5° rotation of the ZOX cross-section during post-processing. Fast Fourier Transform (FFT) with Hanning window is adopted to extract the disturbance amplitude and wave number of the flame perturbation. The effects of spark energy, spark radius and time step on the simulation results are also discussed. The computational methodology is first validated by experimental data at atmospheric condition and then applied to premixed natural gas/air mixtures under elevated temperature and pressure. The results showed that the initial temperature has little effect on the flame morphology, while the crack splitting on the flame front intensifies from the initial stage of flame propagation and the number of cells on the flame surface obviously increases as the initial pressure increases. The initial pressure has a more significant effect on the critical flame radius than the initial temperature. This is because increasing the initial pressure leads to the reduction of flame thickness while both the flame thickness and the density ratio decrease with the increase of initial temperature. Moreover, disturbance energy within the wavenumber range of 4–15 increases significantly with the increase of initial pressure, especially at stoichiometry condition. This is because the restriction effect of flame stretch on flame inherent instability reduces with the increase of initial pressure. [ABSTRACT FROM AUTHOR]