Effects of heat release in a reacting vortex ring

Flame-vortex interactions provide a carefully controllable environment in which fundamental processes relevant to turbulent diffusion flames can be investigated. Here we present microgravity experiments and numerical simulations of a reacting vortex ring that reveal the dominant effects of heat release on the flow, mixing, and combustion processes. Hydrodynamically scaled ring trajectories showed an initial increase in ring speed due to heat release, followed by a large reduction in speed. The enhanced diffusivities due to heat release do not suffice to explain these observations, which appear to be directly connected with dilatation effects. The observed dependence on the fuel volume introduced in the ring during the initial roll-up phase suggests a simple model that reconciles these observations. Numerical simulations of mixture fraction fields and equilibrium temperatures showed that, consistent with this, volume dilatation due to heat release is the primary mechanism that alters the flow and mixing processes in reacting rings over those in isothermal rings. These simulations support the experimentally observed effects but do not explain differences in flame shape and height that appear to be due to radiative heat losses.