Flow field characterization of pressurized sooting swirl flames and relation to soot distributions

Abstract

Mean and instantaneous flow fields were derived for sooting pressurized swirl flames, operated with ethylene/air in an aero-engine model combustor. Stereo particle image velocimetry served to deduce three velocity components and to identify locations of soot based on soot scattering. The measurements complement those of other quantities in the same flames published recently. Flow fields determined for cold and reactive conditions confirm conclusions drawn from application of other laser-based diagnostics: soot is mainly formed in the inner recirculation zone which recirculates reactive, hot unburnt reaction products, and partly transported into the high-velocity in-flow regions. Oxidation air injected after two thirds of the combustor forms a stagnation zone close to the combustor axis and splits into a portion flowing downstream toward the combustor exit and one transported upstream thereby affecting the local gas composition and temperatures in the inner recirculation zone. Analysis of the instantaneous images by proper orthogonal decomposition reveals the existence of a precessing vortex core which impacts the soot distribution. Presence of soot in high-velocity/high strain rate regions where soot formation is unlikely to occur can be explained as a result of transport. Flow field characterization and the correlation with soot presence, in complement of existing data, are expected to provide a valuable contribution to soot model validation.