Void Collapse and Jet Formation:
The impact of a disk on a water surface.
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Faculty of Science and J.M. Burgers center for Fluid Dynamics, University of Twente,
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c i t i e s
o
s
f
= 0 to 5 m/s. The presence of the free surface and the
short duration of the phenomenon suggest that the effects of viscosity can be
neglected during the formation and collapse of the void. An inviscid model can
therefore
be
adopted,
which
boundary integral method. F
is
efficiently
solved
numerically
by
means
of
a
igure 1 shows that the simulations are in excellent
agreement with the experimental void formation and collapse. As can be seen in
F
igure 2, the depth of the void closure divided by the disk radius d /R scales
with the sq
uare root of the F
experiments ( blue error bars)
roude number, defined by F
r = U /gR, for both
and simulations ( red dots) .
As the walls of the void come together on the axis of symmetry at the end of the
collapse,
the
destruction
of
the
radial
liq
uid
momentum
produces
a
large
pressure spike which creates two jets of water, one shooting up straight into the
air ( F
3
igure 3
a) , and one down, piercing the void enclosed by the collapse ( F
igure
b) .
[1] H.J. Melosh, Impact Cratering: A Geologic Process (Oxford University Press, Oxford, 1989)
[2] D. Lohse, R.P.H.M. Bergmann, R. Mikkelsen, C. Zeilstra, D. v/d Meer, M. Versluis, K. v/d
Weele, M.A. v/d Hoef, J.A.M. Kuipers - Impact, preprint (2004)
[3] S. Gaudet - Numerical simulation of circular disks entering the free surface of a fluid, Phys.
Fluids 10, 2489 (1998)
[4] J.W. Glasheen, T.A. McMahon - Vertical water entry of disks at low Froude numbers, Phys.
Fluids 8, 8 (1996)
[5] H.N. Oguz, A. Prosperetti, A.R. Kolaini - Air Entrapment by a falling water mass, J. Fluid
Mech. 294, 181 (1995)
t=-48ms
t=35ms
t=57ms
t=88ms
t=115ms
t=128ms
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