Flame structure of non-forced acoustically driven flames using proper orthogonal decomposition

Chemiluminescence imaging, a common optical diagnostic used to study acoustically driven flames, suffers from poor resolution due to line of sight integration. An Abel transform can be used to extract planar profiles in flames of known symmetry; however, it may be insufficient near the axis of symmetry, for flames with unknown symmetry, and when there are several flame fronts close together. This paper presents the use of three-dimensional proper orthogonal decomposition (POD) to find flame fronts in a premixed methane flame undergoing self-excited thermoacoustic interactions. Three principal modes are found to be sufficient to describe the flame shape. Twodimensional POD was then performed on the flame fronts and the number of modes required to produce the entire reduced data set was found to depend on the Reynolds number of the reactant flow.