Physics of Fluids - Publications

Dynamics of high-speed micro-drop impact: numerical simulations and experiments at frame-to-frame times below 100 ns

Soft Matter 11, 1708–1722 (2015)

Authors

	Claas-Willem Visser
	Philipp Erhard Frommhold
	Sander Wildeman
	Robert Mettin
	Detlef Lohse
	Chao Sun

BibTeΧ

@Article{C4SM02474E,
author ="Visser, Claas Willem and Frommhold, Philipp Erhard and Wildeman, Sander and Mettin, Robert and Lohse, Detlef and Sun, Chao",
title  ="Dynamics of high-speed micro-drop impact: numerical simulations and experiments at frame-to-frame times below 100 ns",
journal  ="Soft Matter",
year  ="2015",
volume  ="11",
issue  ="9",
pages  ="1708-1722",
publisher  ="The Royal Society of Chemistry",
doi  ="10.1039/C4SM02474E",
url  ="http://dx.doi.org/10.1039/C4SM02474E",
abstract  ="Technologies including (3D-) (bio-)printing{,} diesel engines{,} laser-induced forward transfer{,} and spray cleaning require optimization and therefore understanding of micrometer-sized droplets impacting at velocities beyond 10 m s-1. However{,} as yet{,} this regime has hardly been addressed. Here we present the first time-resolved experimental investigation of microdroplet impact at velocities up to V0 = 50 m s-1{,} on hydrophilic and -phobic surfaces at frame rates exceeding 107 frames per second. A novel method to determine the 3D-droplet profile at sub-micron resolution at the same frame rates is presented{,} using the fringe pattern observed from a bottom view. A numerical model{,} which is validated by the side- and bottom-view measurements{,} is employed to study the viscous boundary layer inside the droplet and the development of the rim. The spreading dynamics{,} the maximal spreading diameter{,} the boundary layer thickness{,} the rim formation{,} and the air bubble entrainment are compared to theory and previous experiments. In general{,} the impact dynamics are equal to millimeter-sized droplet impact for equal Reynolds-{,} Weber- and Stokes numbers (Re{,} We{,} and St{,} respectively). Using our numerical model{,} effective scaling laws for the progression of the boundary layer thickness and the rim diameter are provided. The dimensionless boundary layer thickness develops in time (t) according to {,} and the diameter of the rim develops as {,} with drop diameter D0 and inertial time scale [small tau] = D0/V0. These scalings differ from previously assumed{,} but never validated{,} values. Finally{,} no splash is observed{,} at variance with many predictions but in agreement with models including the influence of the surrounding gas. This confirms that the ambient gas properties are key ingredients for splash threshold predictions."}