Detailed numerical simulations of primary atomization of airblasted liquid sheet. (February 2022) - Asuri Mukundan, Anirudh
Abstract: This paper investigates the primary atomization of airblasted liquid sheet using detailed numerical simulations. The atomization of liquid sheet under airblasting conditions involve complex mechanisms and a thorough understanding is necessary. A planar pre-filming airblast atomization configuration have been chosen to study the breakup of liquid sheet/film injected on a solid flat plate. We have investigated an operating point directly relevant for high altitude relight condition of the aircraft. This configuration has been chosen based on the experimental investigation of Gepperth et al. [S. Gepperth, A. Müller, R. Koch, H.-J. Bauer, Ligament and droplet characteristics in pre-filming airblast atomization, Proceedings of the ICLASS, 12th Triennial International Conference on Liquid Atomization and Spray Systems, September 2-6, Heidelberg, Germany, 2012] for the airblast atomization. The numerical simulations have been performed using in-house Navier–Stokes solver that uses consistent mass and momentum flux computation technique. The purpose of this work is to provide a comprehensive database and analyses of the airblast atomization of liquid sheet. This include studies on the effect of velocity profile on the atomization characteristics, occurrence of secondary atomization and drop coalescence, and extraction of near-field atomization characteristics. The qualitative analyses of the results from the simulations showed that there are two major atomization mechanisms of liquid film breakup — sheet/bag breakup and ligament breakup. The drop diameter and velocity distributions computed from the simulations was found to be of the same order of magnitude although under-predicting the experimental data. Based on the atomized drop data, both the secondary atomization and drop coalescence have been observed to occur in the simulations. The quantitative analyses of the near-field liquid ligaments results revealed the lengths of these ligaments are of the same order of magnitude as the experimental data while an under-prediction in the ligament velocity has been observed. Finally, an excellent agreement between simulations and experimental data has been found for the Sauter Mean Diameter (SMD) of the atomized droplets. Highlights: Hybrid treatment of liquid/gas multiphase interface using moment of fluid (MOF) and level set frameworks. Novel study of the effect of inlet velocity profile for liquid fuel and air investigated. Two prominent atomization mechanisms found — sheet breakup and ligament breakup. Identified the presence and occurrence of secondary atomization and drop coalescence. Novel study to extract near-field ligament data that agrees satisfactorily with experimental measurements.