Precursor Coherent Flow Structures and Droplet Dispersion Relevant for the Stabilization of Swirling Lifted Spray Flame on a Bluff Body Burner

Abstract

We investigate the precursor coherent flow structures and their interactions with spray that are responsible for the stabilization of lifted spray flames of Jet A1 gel fuel on a bluff body–assisted burner of low blockage ratio. Our approach is based on the description of experimental observations of the cold spray and swirling lifted flames on a laboratory burner, followed by the cold flow computations of gas and liquid phase flow fields carried out on the same burner. Anisotropy of the highly swirling and three–dimensional turbulent flow and inherently high pressure strain were resolved using the quadratic pressure strain–Reynolds stress model, followed by computations of droplet trajectories using their Lagrangian discrete phase and one-way coupled description. Same flow was also computed as a large eddy simulation (LES) while retaining the one-way coupling. The flow and droplet dispersion models were validated using experimental data, independent validation test data, and single-grid LES. Our emphasis on resolving large–scale coherent structures during modeling and rigorous validation tests yields accurate predictions of the flow structures, lift–off height, undisturbed spray height, and spray droplet distributions. Gas–phase flow field of a compound jet system comprising annular combustion air and round spray jet was found to be dominated by the flow structures associated with the round jet. A complex system of vortices that controlled the distribution and mixing of the dominant 3–23 μm size fuel droplets with combustion air in the flame stabilization region was also extracted and described. Cold flow field computed by LES provided an accurate prediction of streamline curvature caused by loss of coherence of a three-vortex system influencing the spray jet. © 2023, The Author(s), under exclusive licence to Springer Nature B.V.