The liquid atomization process relies on the disturbance of the liquid surface by various forces. In the case of "flow-blurring" (FB) atomization, this is achieved by inducing turbulence near the liquid channel exit. In this study, we analyze the underlying dynamics of these coherent turbulent structures and their role in the primary atomization within the FB regime. For that purpose, Smoothed Particles Hydrodynamics (SPH) simulations have been conducted using the geometry of an FB atomizer, which was also studied experimentally. An in-house developed visualization and data exploration platform (postAtom) was used to capture the time-resolved, Lagrangian coherent structures (LCSs) via the finite-time Lyapunov exponent (FTLE) fields. The results indicate that the design of the mixing chamber can trigger an oscillatory behavior at the nozzle exit, which has a direct impact on the evolution of the micro-ligaments and the consecutive primary atomization. It is further shown how the FTLE fields can be used as a guide to optimize the nozzle geometry.

In this work, we will identify a novel relation between Smoothed Particle Hydrodynamics (SPH) and explicit large eddy simulation using a coarse-graining method from non-equilibrium molecular dynamics. While the current literature points at the conclusion that characteristic SPH issues become restrictive for subsonic turbulent flows, we see the potential to mitigate these SPH issues by explicit subfilter stress modeling. We verify our theory by various simulations of homogeneous, isotropic turbulence at [Formula: see text] and compare the results to a direct numerical simulation [T. Dairay et al., “Numerical dissipation vs subgrid-scale modelling for large eddy simulation,” J. Comput. Phys. 337, 252–274 (2017)]. Although the simulations substantiate our theory, we see another issue arising, which is conceptually rooted in the particle itself, termed as particle duality. Finally, we conclude our work by acknowledging SPH as a coarse-graining method for turbulent flows, highlighting its capabilities and limitations.

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In this work a numerical investigation of the sensitivities of the spray dispersion to different droplet starting parameters in a realistic three-dimensional fuel injector geometry is presented. The simulations are carried out using an Euler-Lagrange method. An extended version of the primary atomization model PAMELA [1,2] is used to predict the droplet diameter and to set the droplet starting conditions. Spray characteristics are compared to experimental data [3]. Thereby, a strong influence of the initial droplet velocities, the recirculation zone, the precessing vortex core as well as the turbulence modelling approach on the spray dispersion was identified. Droplet starting conditions which provide good agreement to the experimental data are determined. The study demonstrates that the presented approach is a viable option to predict the spray dispersion in combustors. Moreover, valuable insights on necessary improvements for modeling primary atomization are given.

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