Single droplet impacts onto thin wall-films are a common phenomenon in many applications. For sufficiently high impact velocities, the droplet impact process consists of three phases, i.e., initial contact stage, droplet deformation with radial momentum transfer inducing an upward rising lamella, and crown propagation. Here, we present the results of a combined numerical and experimental study focusing on the early dynamics of the impact process. Specifically, the effects of the initial droplet shape, wall-film thickness, and contact line motion are analyzed. Prior to impact, an oblate spheroidal droplet shape was observed. Using direct numerical simulation, we show that the droplet shape affects the impact dynamics only during the first two phases, as it is one of the key parameter influencing the correct prediction of the impact zone. The contact line propagation is described by a square-root-time dependence R ¯ CL = α τ for both, dry and wetted surfaces. On dry surfaces, the advancement of the contact line is determined by the rolling motion of the truncated droplet. On wetted surfaces, the value of the α-parameter is controlled by two concurrent effects, namely, rolling motion and wall-film inertia. For impact onto thin films, the rolling motion prevails. With increasing wall-film height, the droplet penetrates into the soft substrates and wall-film inertia becomes the controlling factor. These insights into the early impact dynamics on wetted surface are important for the formulation of a unified modeling approach.

1.
R.
Xu
,
G.
Wang
, and
P.
Jiang
, “
Spray cooling on enhanced surfaces: A review of the progress and mechanisms
,”
J. Electron. Packag.
144
,
010802
(
2022
).
2.
C.
Eisenbarth
,
W.
Haase
,
L.
Blandini
, and
W.
Sobek
, “
Potentials of hydroactive lightweight façades for urban climate resilience
,”
Civil Eng. Des.
4
,
14
24
(
2022
).
3.
A. L.
Yarin
, “
Drop impact dynamics: Splashing, spreading, receding, bouncing…
,”
Annu. Rev. Fluid Mech.
38
,
159
192
(
2006
).
4.
G.
Liang
and
I.
Mudawar
, “
Review of mass and momentum interactions during drop impact on a liquid film
,”
Int. J. Heat Mass Transfer
101
,
577
599
(
2016
).
5.
C.
Josserand
and
S. T.
Thoroddsen
, “
Drop impact on a solid surface
,”
Annu. Rev. Fluid Mech.
48
,
365
391
(
2016
).
6.
A.
Geppert
,
A.
Terzis
,
G.
Lamanna
,
M.
Marengo
, and
B.
Weigand
, “
A benchmark study for the crown-type splashing dynamics of one- and two-component droplet wall-film interactions
,”
Exp. Fluids
58
,
1
27
(
2017
).
7.
H. M.
Kittel
,
I. V.
Roisman
, and
C.
Tropea
, “
Splash of a drop impacting onto a solid substrate wetted by a thin film of another liquid
,”
Phys. Rev. Fluids
3
,
073601
(
2018
).
8.
B.
Stumpf
,
J.
Hussong
, and
I. V.
Roisman
, “
Drop impact onto a substrate wetted by another liquid: Flow in the wall film
,”
Colloids Interfaces
6
,
58
(
2022
).
9.
S.
Shaikh
,
G.
Toyofuku
,
R.
Hoang
, and
J. O.
Marston
, “
Immiscible impact dynamics of droplets onto millimetric films
,”
Exp. Fluids
59
,
7
(
2018
).
10.
B.
Stumpf
,
J. H.
Ruesch
,
I. V.
Roisman
,
C.
Tropea
, and
J.
Hussong
, “
An imaging technique for determining the volume fraction of two-component droplets of immiscible fluids
,”
Exp. Fluids
63
,
114
(
2022
).
11.
I. V.
Roisman
,
N. P.
van Hinsberg
, and
C.
Tropea
, “
Propagation of a kinematic instability in a liquid layer: Capillary and gravity effects
,”
Phys. Rev. E
77
,
046305
(
2008
).
12.
I. V.
Roisman
, “
Inertia dominated drop collisions. II. An analyrical solution of the Navier-Stokes equations for a spreading viscous film
,”
Phys. Fluids
21
,
052104
(
2009
).
13.
A. L.
Yarin
and
D. A.
Weiss
, “
Impact of drops on solid surfaces: Self-similar capillary waves, and splashing as a new type of kinematic discontinuity
,”
J. Fluid Mech.
283
,
141
173
(
1995
).
14.
X.
Gao
and
R.
Li
, “
Impact of a single drop on a flowing liquid film
,”
Phys. Rev. E
92
,
053005
(
2015
).
15.
M. F.
Trujillo
and
C. F.
Lee
, “
Modeling crown formation due to the splashing of a droplet
,”
Phys. Fluids
13
,
2503
2516
(
2001
).
16.
B. R.
Mitchell
,
J. C.
Klewicki
,
Y. P.
Korkolis
, and
B. L.
Kinsey
, “
The transient force profile of low-speed droplet impact: Measurements and model
,”
J. Fluid Mech.
867
,
300
322
(
2019
).
17.
Y.
Yu
and
C.
Hopkins
, “
Experimental determination of forces applied by liquid water drops at high drop velocities impacting a glass plate with and without a shallow water layer using wavelet deconvolution
,”
Exp. Fluids
59
,
84
(
2018
).
18.
A.
Geppert
,
D.
Chatzianagnostou
,
C.
Meister
,
H.
Gomaa
,
G.
Lamanna
, and
B.
Weigand
, “
Classification of impact morphology and splashing/deposition limit for n-hexadecane
,”
Atomiz. Spr.
26
,
983
1007
(
2016
).
19.
G.
Whitham
,
Linear and Nonlinear Waves
(
John Wiley & Sons, Inc
.,
1974
).
20.
G.
Lamanna
,
A.
Geppert
,
R.
Bernard
, and
B.
Weigand
, “
Drop impact onto wetted walls: An unsteady analytical solution for modelling crown spreading
,”
J. Fluid Mech.
938
,
A34
(
2022
).
21.
J.
Philippi
,
P.-Y.
Lagrée
, and
A.
Antkowiak
, “
Drop impact on a solid surface: Short-time self-similarity
,”
J. Fluid Mech.
795
,
96
135
(
2016
).
22.
A. K.
Geppert
, “
Experimental investigation of droplet Wall-Film interaction of binary systems
,” Ph.D. thesis (
University of Stuttgart
,
2019
).
23.
B.
Lafaurie
,
C.
Nardone
,
R.
Scardovelli
,
S.
Zaleski
, and
G.
Zanetti
, “
Modelling merging and fragmentation in multiphase flows with surfer
,”
J. Comput. Phys.
113
,
134
147
(
1994
).
24.
W. J.
Rider
and
D. B.
Kothe
, “
Reconstructing volume tracking
,”
J. Comput. Phys.
141
,
112
152
(
1998
).
25.
K.
Eisenschmidt
,
M.
Ertl
,
H.
Gomaa
,
C.
Kieffer-Roth
,
C.
Meister
,
P.
Rauschenberger
,
M.
Reitzle
,
K.
Schlottke
, and
B.
Weigand
, “
Direct numerical simulations for multiphase flows: An overview of the multiphase code FS3D
,”
Appl. Math. Comput.
272
,
508
517
(
2016
).
26.
S.
Fest-Santini
,
J.
Steigerwald
,
M.
Santini
,
G. E.
Cossali
, and
B.
Weigand
, “
Multiple drops impact onto a liquid film: Direct numerical simulation and experimental validation
,”
Comput. Fluids
214
,
104761
(
2021
).
27.
J.
Steigerwald
,
M.
Ibach
,
J.
Reutzsch
, and
B.
Weigand
, “
Towards the numerical determination of the splashing threshold of two-component drop film interactions
,” in
High Performance Computing in Science and Engineering '20
(
Springer International Publishing
,
2021
), pp.
261
279
.
28.
J.
Steigerwald
,
A.
Geppert
, and
B.
Weigand
, “
Numerical study of drop shape effects in binary drop film interactions for different density ratios
,” in
Proceedings ICLASS 2021. 15th Triennial International Conference on Liquid Atomization and Spray Systems, Edinburgh, UK, 29 August–2 September 2021
(ICLASS, Edinburgh,
2021
).
29.
R.
Clift
,
J. R.
Grace
, and
M. E.
Weber
,
Bubbles, Drops, and Particles
(
Academic Press, Inc
.,
1978
).
30.
G. E.
Cossali
,
M.
Marengo
,
A.
Coghe
, and
S.
Zhdanov
, “
The role of time in single drop splash on thin film
,”
Exp. Fluids
36
,
888
900
(
2004
).

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