ISBN 9783843957496

978-3-8439-5749-6, Reihe Thermodynamik

Jonathan Lukas Stober
Oblique Droplet Impact onto a Thin Wall Film

186 Seiten, Dissertation Universität Stuttgart (2026), Softcover, A5

Zusammenfassung / Abstract

Sprays are widely used in industrial and environmental applications, including spray coating, medical inhalers, and cleaning or cooling processes. In these cases, droplets impact obliquely onto already wetted surfaces, and their impact dynamics are highly relevant. However, the flow development during oblique impacts remain insufficiently understood, and a comprehensive classification of crown formation and splashing regimes is still lacking.

This thesis addresses these gaps by combining systematic experiments with highly resolved Direct Numerical Simulations. More than 600 droplet impacts over a wide range of impact angles and Weber numbers provide a broad experimental basis. The simulations, performed with the in-house code FS3D, complement these data by resolving the full three-dimensional flow field and are used to explain the mechanisms underlying the observed phenomena.

A previously unreported oblique mechanism of crown formation is identified experimentally in the early stages after impact. This behaviour is explained by the numerical simulations, which reveal that the rear crown collides with the droplet bulk and therefore develops in a fundamentally different manner. Based on the large experimental database, distinct splashing regimes are observed and classified according to finger formation and the detachment mechanisms of secondary droplets from the crown. Mathematical threshold criteria are derived to separate these regimes, resulting in a comprehensive regime map.

The numerical results provide detailed insight into the mechanisms underlying the experimental observations. The wall film flow driving crown spreading is analysed in detail. By systematically varying viscosity and wall boundary conditions, wall friction within the inner film is identified as the dominant factor driving its development. In addition, the simulations quantify and characterise the asymmetry of the velocity field within the film under oblique impact conditions.