ISBN 978-3-8439-5667-3

978-3-8439-5667-3, Reihe Thermodynamik

Matthias Ibach
Numerical Investigation of Droplet Oscillation and Grouping Phenomena

214 Seiten, Dissertation Universität Stuttgart (2025), Softcover, A5

Zusammenfassung / Abstract

Multiphase flows involving spray systems and droplet streams play a key role in technical, medical and industrial applications. Understanding droplet behavior, including deformation, motion and interaction, is crucial for optimizing these systems. Simplified models, such as monodisperse droplet streams, allow detailed studies of oscillation, motion and grouping.

The primary objective of this thesis is to deepen the fundamental understanding of droplet oscillation, grouping and the influence of deformed, oscillating droplets on droplet motion in streams. This is done using Free Surface 3D (FS3D), a high-resolution Direct Numerical Simulation (DNS) framework employing the Volume-of-Fluid method (VOF).

For droplet oscillation, the work explores oscillation modes, damping behavior, frequencies and mode coupling for various initial conditions, revealing deviations from linear theory, especially for large amplitudes, high viscosities and initial higher harmonics. Non-Newtonian effects are studied, highlighting transient behavior and time lags between structural evolution and oscillatory motion. Jacobi Sets and STL Decomposition help reveal fluid-microstructure interactions. A novel post-processing method quantifies oscillation metrics and energy budgets, uncovering a collapse of prolate and oblate times over energy across a wide range of conditions.

For droplet grouping, simulations are validated against experiments, and parametric studies assess the effects of initial droplet separation and Reynolds number. Co-planar arrangements show significant deviations from single streams when lateral distances are below five diameters. A derived scaling law for grouping time reveals a linear trend across all relevant parameters. Neighboring droplets strongly influence oscillation, with only slight frequency shift but a significant decrease in damping at higher velocities and closer spacing, highlighting the importance of considering deformed droplets in grouping dynamics.