Results from numerical simulations of the diffusion flame-vortex ring interaction

Flame-vortex interactions are canonical configurations that allow access to the fundamentals of combustion science issues to be investigated under more permissible conditions than in practical combustion devices. Numerical simulations of reacting vortex rings were conducted to assess the effects of combustion heat release, fuel volume, and ring circulation on the flame structure and ring dynamics for methane-air combustion. Effects of ring circulation and fuel volume on concentrations of major and minor species, and temperature field were also examined. Fluid dynamics-combustion coupling was incorporated by using the conserved scalar approach in which the chemical species and temperature are functions of the conserved scalar (e.g. mixture fraction) and the scalar dissipation rate. Combustion heat release modified the ring structure by causing a radial expansion, and dilatation had the effect of increasing the ring speed in the early stage of interaction. However, dilatation was responsible for the drastic decrease in ring speed in the late stage of interaction. Oxygen concentration was not present inside the ring, and this suggested that a diffu- sion-limited reaction is adequate in modeling the fuel consumption time. Water and carbon dioxide were found near the hot reaction zones, however, carbon dioxide was not present inside the ring where fuel has not yet been consumed by the reaction. The increase in fuel volume while keeping the ring circulation constant did not considerably modify the concentration fields of chemical species and temperature fields. However, the increase in ring circulation while keeping the fuel volume constant led to an increase in the production of minor species (OH, CH and HCO) along the forward stagnation point of the reacting vortex rings.