Toward direct numerical simulation of high speed droplet impact

Abstract

When a liquid drop impacts a solid surface or a liquid film, several outcomes are possible. In particular, splashing phenomena can exhibit complex behaviors, like the formation of very thin crowns and emission of small droplets. Underlying mechanisms are hard to elucidate, partly due to the difficulty for current experimental devices to access to the very small length scales involved. Here, we use direct numerical simulation to explore low and high velocity drop impact phenomena. We show that classical incompressible two-phase methods can be sufficient to address low energy impacts and take into account wetting phenomena. However, dedicated robust and conservative methods are needed to simulate splashing phenomenon at higher velocities. In our test cases, we show that an impact on a thick liquid film exhibits thick crown formation and delayed splashing. On a dry wall, on the other hand, splashing phenomenon can be difficult to reproduce even with high velocity impacts. We show however how a higher value of the surrounding air density may trigger splashing. The presence of a even very thin liquid film on the wall strongly modifies impact outcome, forcing the ejection of a thin crown and subsequent secondary droplet emission.

Air film evolution during droplet impact onto a solid surface

“…The DCA is mainly influenced by the droplet diameter and impact velocity, which is a result of the competitions among the inertia [39][40][41] , the viscosity of the droplet [39][40][41][42] , the wettability of the substrate [40][41][42][43][44] and the liquid-gas surface tension 40,41,43,44 . The DCA has been shown to capture well the droplet impact dynamics such as the maximum spreading diameter coefficient, up to the point of splashing threshold 42,45,46 . Although it's still not understood clearly, it is generally agreed that the DCA is a function of the contact line movement speed 38,47 .…”

A new efficient momentum preserving Level-Set/VOF method for high density and momentum ratio incompressible two-phase flows

“…Differently from the Rudman's algorithm, no subgrid reconstruction is needed to calculate the sub-cells densities appearing in Eq.s ( 24) and (25). Indeed, as can be seen in Fig.…”

“…. The shaded areas correspond to the sub-grid volume fraction used to compute subgrid densities in Eq.s (24) and (25). The red marks show the intersections between the PLIC reconstructions and the sub-cell faces.…”

“…The whole algorithm has been implemented and tested in the ONERA DY-JEAT code (see Couderc [22], Zuzio and Estivalèzes [23], Zuzio et al [24] and Xavier et al [25]). Several test cases are presented, from simpler academical case to a realistic atomizations application.…”

Editorial

“…Soligo et al [6] present a diffuse-interface approach to model the surfactant dynamics close to an interface and studies its effect on droplet deformation. Numerical methods for the simulations of high-speed droplet impact and the motion of a solid particle in a viscous flow are presented in [7] and [8]. Finally, Vaitukatis et al [9] present an application of transport and absorption for a specific application such as pharmaceutical tablets.…”