A round liquid jet with density ρ, surface tension σ and diameter D0 impacting a solid
circular surface at normal incidence with velocity U0 takes the form of a radially
expanding sheet whose thickness decreases with distance from the impact point. When
the sheet develops in a still environment with density ρa = αρ, it destabilizes, provided
the impacting Weber number We = ρU20D0/σ is larger than about 40α−1/2, as a result
of a shear instability with the surrounding medium, in a sinuous, flag-like motion.
We show how the instability properties set both the radial extent of the liquid sheet
and the drop formation process at its rim. The shear instability gives the liquid a
flag-like motion, ultimately triggering a Rayleigh–Taylor instability at the rim of the
sheet which disintegrates, at the radial location R, into disjointed droplets of size d
R/D0 ∼ α−2/3
d/D0 ∼ α−2/3We−1.
The features of the sheet instability, its radius and the droplet sizes are determined
experimentally for a broad range of control parameters, using different liquids and