Analysis of the dynamics at the Base of a Lifted Strongly Buoyant Jet Flame Using Direct Numerical Simulation

Non-premixed jet flames represent a generic flame configuration with high relevance in many

combustion devices. The present work computationally investigates the case of a strongly

buoyant non-premixed turbulent jet flame using Direct Numerical Simulation (DNS). The

simulation results unveil a weak upstream effect of the flame on the non-burning region ahead

of the flame base. A comparatively more substantial effect of the flame is seen in the largescale

motion, which evolves under the influence of the periodic formation, growth, and

departure of large bulb-shaped low-density structures at the flame base, as it is also seen in

experiments. The analysis of the dominant stability mechanism of the flame base essentially

supports the established concept of edge-flame propagation. Moreover, the buoyancy-driven

large-scale flow structures temporally generate a further highly critical scenario, where large

circumferential sections of the flame base recede deeply downstream, which is shown to be

triggered by high local values of the scalar dissipation rate. With this particular scenario the

present work does not only bring to light an important stabilization mechanism governed by

large three-dimensional structures, it also recalls the relevance of the scalar dissipation rate,

whose effect is often discarded in the commonly accepted theories on flame stabilization.