On colliding spherical flames: Morphology, corner dynamics, and flame-generated vorticity

The collision of two identical spherical flames was studied for its relevance in flame interactions in various practical situations including those within turbulent flames. Experimentally, premixtures of fuel (H₂, C₃H₈) and oxidizer were ignited by two synchronized sparks in a closed chamber under atmospheric pressure, with the subsequent flame-front evolution tracked by a Schlieren system with high-speed camera, as well as computationally simulated. Results show that development of the morphology of flame collision can be distinguished in three stages: independent propagation, strong interaction with flattened interfaces, and corner dynamics after merging of the interfaces. It is further demonstrated that propagation of the flame corner is controlled by the interacting mechanisms of preferential diffusion and kinematic restoration, that vorticity of considerable strength is generated downstream of the corner flame segment, and that the kinetic energy of the flame-generated vorticity is substantial as compared to those of the Kolmogorov eddies such that it could have strong influence on the turbulence energy spectrum and flame burning rate.