arXiv subjects

Philipp Brockmann

Publications and source records attributed to Philipp Brockmann.

3 recordsLinked to original sources

arXiv2025

On the vortex ring formation and mixing in thin films upon droplet impact

When a droplet impacts a liquid film, a vortex ring form and govern momentum and species transport. We experimentally investigate vortex ring formation, propagation and instability during droplet impact onto liquid films, with particular emphasis on vortex ring-wall interactions. Particle image velocimetry and laser-induced fluorescence are used to study the effects of Reynolds number Re, Weber number We and dimensionless film thickness \delta over ranges Re \leq 3900, We \leq 61 and 0.09 \leq \delta \leq 1.35. As film thickness decreases, a transition from a single axisymmetric vortex ring to azimuthally unstable, multi-vortex structures is observed. A regime map in Re-\delta space is constructed, showing that vortex ring instabilities occur at lower Re for thinner films, while no instabilities are detected for thick films up to the highest Re studied. The azimuthal wave number increases with Re and decreases with \delta. Thinner films exhibit faster decay of primary vortex ring circulation due to wall interactions, accompanied by the formation of secondary vortex ring at lower Re. An empirical model is proposed to predict the temporal evolution of total vortex ring circulation, accounting for both generation and decay.

physics.flu-dyn↗

arXiv2024

Dewetting Fingering Instability in Capillary Suspensions: Role of Particles and Liquid Bridges

This study investigates the fingering instability that forms during stretching of capillary suspensions with and without added nanoparticles. The dewetting process is observed using a transparent lifted Hele-Shaw cell. The liquid bridge is stretched under constant acceleration, and the resulting instability patterns are recorded using two high-speed cameras. Finger-like structures, characteristic of the Saffman-Taylor instability are observed. The total length of the dendrites and the intersecting number of branches are quantified. We reveal the roles of microparticles, nanoparticles, and the secondary liquid during the fingering instability. The addition of microparticles to pure liquid enhanced finger length due to increased particle interactions and nucleation sites for bubbles. The addition of secondary fluid reduces fingering length by forming a strong interparticle network. Incorporation of nanoparticles induces an early onset of cavitation and enhances fingering instability. However, nanoparticles make the capillary suspensions' overall microstructure more homogeneous, reduce the sample variation in fingering patterns, and promote the even distribution of gel on both slides during splitting. These findings highlight the complex interactions governing dewetting in capillary (nano)suspensions. This knowledge has potential applications in microfluidics, 3D printing, and thin-film coatings, where controlling dewetting is crucial.

cond-mat.soft↗

arXiv2020

On the calibration of Astigmatism particle tracking velocimetryfor suspensions of different volume fractions

In the present study we demonstrate for the first time how Astigmatism Particle Tracking Velocimetry (APTV) can be utilized to measure suspensions dynamics. Measurements were successfully performed in monodisperse, refractive index matched suspensions of up to a volume fraction of $Φ=19.9\%$. For this, a small percentage of the particles is labeled with fluorescent dye acting as tracers for the particle tracking procedure. Calibration results show, that a slight deviation of the refractive index of liquid and particles leads to a strong shape change of the calibration curve with respect to the unladen case. This effect becomes more severe along the channel height. To compensate the shape change of the calibration curves the interpolation technique developed by Brockmann et al. (Experiments in Fluids, 61(2), 67, \citeyear{brockmann2020utilizing}) is adapted. Using this technique, the interpolation procedure is applied to suspensions with 6 different volume fractions ranging from $Φ<0.01\%$ to $Φ=19.9\%$. To determine the effect of volume fraction on the perfomance of the method, the depth reconstruction error $σ_z$ and the measurement volume depth $Δz$, obtained in different calibration measurements, are estimated. Here, a relative position reconstruction accuracy of $σ_z$/$Δz$=0.90\% and $σ_z$/$Δz$=2.53\% is achieved for labeled calibration particles in dilute ($Φ<0.01\%$) and semi-dilute ($Φ\approx19.9\%$) suspensions, respectively. The measurement technique is validated for a laminar flow in a straight rectangular channel with a cross-sectional area of 2.55$\times$30\,mm$^2$. Uncertainties of 1.39\% and 3.34\% for the in-plane and 9.04\% and 22.57\% for the out-of-plane velocity with respect to the maximum streamwise velocity are achieved, at solid volume fractions of $Φ<0.01\%$ and $Φ=19.9\%$, respectively.

physics.flu-dyn↗