Numerical investigation of spreading time in droplet impact with spherical surfaces: from physical analysis to data-driven prediction model
Abstract
Spreading time, the time that an impacting droplet attains the maximum wetting area on a
solid surface, plays a critical role in many engineering applications particularly where heat
transfer or chemical reactions are involved. Although the impact dynamics of a droplet
significantly differ across the different spreading regimes depending on various collision
parameters, it still remains unclear (i) how the spreading time changes for each spreading
regime, and (ii) how the target curvature can affect the spreading time. In the present study,
the spreading time during droplet impact on a spherical target is systematically studied at the
three different spreading regimes for a wide range of impact parameters (Weber number,
equilibrium contact angle, Ohnesorge number and droplet-to-target size ratio). The changes
of spreading time depending on the impact parameters and underlying physical mechanisms
are analyzed in detail at the level of three different spreading regimes. Our results show that
the spreading time, proper time scales, dominant impact parameters and associated physical
behaviors all significantly and non-linearly change across the three spreading regimes. An
improved prediction model for the spreading time is also proposed for each regime, which is
now based on only the controllable variables and has an explicit form. The effect of target
curvature on the spreading time is further investigated, and finally, a data-driven prediction
model is proposed to represent the complicated and non-linear nature of the spreading time
broadly across the three spreading regimes.
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