Local statistics of laminar expanding flames subjected to Darrieus–Landau instability

We, herein, report an experimental study to investigate the role of local flamefront dynamics on the propagation and acceleration of cellularly unstable premixed expanding laminar flames. Using simultaneous Mie-scattering imaging and Particle Image Velocimetry, we measured the flame edge location and its adjacent flow field, which were subsequently processed to quantify the evolution of the probability density functions (pdfs) of flow velocities, curvature, normal strain rate and tangential strain rate. We showed that appropriate normalizaton of the measured quantities can unify the data from different pressures when identified with the corresponding Peclet number, defined as the ratio of the flame radius to the flame thickness. Since the flamefront is stable and smooth at lower Peclet numbers, the flame-induced flow field and stretch rates are almost uniform over the flamefront, resulting in narrow pdfs. At higher Peclet numbers, however, the flame becomes progressively more wrinkled and hence the variations in the local quantities increase leading to wider pdfs. Furthermore, while the mean curvature was found to be inversely proportional to the mean flame radius and insensitive to the cellular structure, the mean normal strain rate was strongly influenced by the cellular structure.