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.