Elias Trautner

The present article is concerned with the modeling of primary atomization in Eulerian-Lagrangian Large Eddy Simulation of liquid jet breakup. Recent numerical studies have demonstrated that spray atomization does not strictly follow a large-to-small breakup cascade. Instead, numerous small droplets can directly be generated by the core jet. As these cannot be resolved in Large Eddy Simulations using interface capturing methods for primary atomization, modeling their formation by releasing small Lagrangian particles from the core jet might improve the predictive capabilities of such simulations. This study discusses a corresponding model proposed in the literature and demonstrates its application for a Large Eddy Simulation of a complex Diesel-like spray. The results indicate a promising performance, but also highlight the need for further investigation.

This study is concerned with Large Eddy Simulation of liquid jet atomization using a two-way coupled Eulerian-Lagrangian multiscale approach. The proposed framework combines Volume-of-Fluid interface capturing with Lagrangian Particle Tracking. The former is used to compute the core jet and large liquid elements in the near-nozzle region, whereas the latter is used to track the large number of small droplets in the dilute downstream region of the spray. The convective and surface tension sub-grid scale terms arising in the context of two-phase flow LES are closed using suitable models, and secondary atomization is considered by employing a modified version of the Taylor Analogy Breakup model. The introduced framework is used to simulate an oil-in-air atomization as well as the Diesel-like Spray A test case of the Engine Combustion Network. Compared to previous studies based on Eulerian-Lagrangian methods, the present work stands out for the high-fidelity numerical approach, the complex test cases and the detailed comparison of the results to experimental data, which indicates a promising performance.

We study the segregation of emulsions in decaying turbulence using direct numerical simulations in combination with the volume of fluid method. To this end, we generate emulsions in forced homogeneous isotropic turbulence and then turn the forcing off and activate the gravitational acceleration. This allows us to study the segregation process in decaying turbulence and under gravity. We consider non-iso-density emulsions, where the dispersed phase is the lighter one. The segregation process is driven by both the minimization of the potential energy achieved by the sinking of the heavier phase as well as the minimization of the surface energy achieved by coalescence. To study these two processes and their impacts on the segregation progress in detail, we consider different buoyancy forces and surface tension coefficients in our investigation, resulting in five different configurations. The surface tension coefficient also alters the droplet size distribution of the emulsion. Using the three-dimensional simulation results and the monitored data, we analyze the driving mechanisms and their impact on the segregation progress in detail. We propose a dimensionless number that reflects the energy release dominating the segregation. Moreover, we evaluate the time required for the rise of the lighter phase and study correlations with the varied parameters: gravitational acceleration and surface tension coefficient.