The large-scale turbulent structure of nonpremixed planar jet flames

A comparative study was conducted of the large-scale turbulent structure of nonpremixed planar jet flames and nonreacting planar jets of varying density. The diagnostic techniques used included planar laser-induced fluorescence of OH and planar laser Mie scattering (PLMS) from alumina particles seeded into the jet fluid. The PLMS imaging shows that the nonreacting jets at all density ratios studied exhibit large-scale organized motions as observed in previous studies at a density ratio of unity. Such organized structures are not nearly as dominant in the jet flames at comparable local Reynolds numbers. To quantitatively investigate the large-scale motions, ensembles of PLMS images were used to compute root-mean-square (RMS) intermittency fields. The RMS intermittency profiles (normalized by the local jet width) are very similar for all of the nonreacting cases, while the flame profile was considerably narrower. Furthermore, plan view PLMS images reveal quasi-two-dimensional organization for the nonreacting case, but more random three-dimensional structure for the flame. These differences argue for the substantial modification of the large-scale turbulent structure owing to the presence of the flame, and do not appear to be due to global Reynolds number effects or global density changes resulting from heat release.