A comparative study of DNS of airblast atomization using CLSMOF and CLSVOF methods

Abstract : The results from direct numerical simulations (DNS) of planar pre-filming airblast atomization are presented in this paper. The configuration of the airblast atomization is inspired from a published experimental configuration of Gepperth et al (2012, "Ligament and Droplet Characteristics in Prefilming Airblast Atomization", ICLASS 2012). The simulations have been performed using our in-house Navier-Stokes solver ARCHER. Two DNS have been performed each respectively using coupled level moment of fluid (CLSMOF) and coupled level set volume of fluid (CLSVOF) methods for liquid/gas interface reconstruction. The operating point investigated in the simulations correspond to aircraft altitude relight conditions. The DNS data are post-processed consistent to that of the experimental data to extract droplet and ligament statistics. The droplet diameter distribution from the simulations is found to be having satisfactory agreement with the experimental data. Two breakup mechanisms of atomization are observed: sheet breakup producing small droplets and ligament breakup producing medium and bulgy droplets. The CLSMOF method is observed to produce more medium and bulgy droplets owing to dominant ligament breakup while CLSVOF method produced more number of small droplets owing to predominant sheet breakup mechanism. A good agreement was found between simulations and experiments for Sauter Mean Diameter (SMD) of the droplets. The droplet diameter distribution from the simulations are found to under-predict the peak of the distribution but displays similar profile as that of the experiments. The droplet velocity distribution from the simulations is found to agree well with that of the experiments. The liquid ligaments formed at the trailing edge of the pre-filmer plate are characterized by their lengths. The breakup length of the ligaments, defined as arithmetic mean of the ligament lengths, computed from the simulations agree satisfactorily with the value computed from the experimental data.