Numerical simulations were conducted to investigate drop impingement and splashing on both dry and wet surfaces at impact velocities greater than 50 m/s with the consideration of the effect of surrounding air. The Navier-Stokes equations were solved using the variable density pressure projection method on a dynamic block structured adaptive grid. The moment of fluid method was used to reconstruct interfaces separating different phases. A dynamic contact angle model was used to define the boundary condition at the moving contact line. Simulations showed that lowering the ambient gas density can suppress dry surface splashing, which is in agreement with the experiments. A recirculation zone was observed inside the drop after contact: a larger recirculation zone was formed earlier in the higher gas density case than in the lower gas density case. Increasing gas density also enhances the creation of secondary droplets from the lamella breakup. For high speed impact on a dry surface, lowering ambient gas density attenuates splashing. However, ambient air does not significantly affect splashing on a wet surface. Simulations showed that the splashed droplets are primarily from the exiting liquid film.

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A moment of fluid method is presented for computing solutions to incompressible multiphase flows in which the number of materials can be greater than two. In this work, the multimaterial moment-of-fluid interface representation technique is applied to simulating surface tension effects at points where three materials meet. The advection terms are solved using a directionally split cell integrated semi-Lagrangian algorithm and the projection method is used to evaluate the pressure gradient force term. The underlying computational grid is a dynamic block structured adaptive grid. The new method is applied to multiphase problems illustrating contact line dynamics, triple junctions, and encapsulation in order to demonstrate its capabilities. Examples are given in 2D, 3D axisymmetric (R-Z), and 3D (X-Y-Z) coordinate systems.

We numerically investigate high-speed drop impact on thin liquid films with a focus on oblique impact. The flow behavior is described by solving the incompressible Navier-Stokes equations using the variable density pressure projection method. The phase interfaces are captured using the momentof-fluid method. The numerical method is validated against experiments and theoretical predictions. Our study on high-speed oblique impact reveals that the tangential velocity can significantly alter impact phenomena: a higher tangential velocity leads to a lower lamella height and radius on the side behind the advancing drop, and the higher tangential velocity also leads to stronger vortices at the drop and film interface due to Kelvin-Helmholtz instability. Our investigation on the effect of liquid film thickness shows that a thinner liquid film leads to an earlier crown breakup. Last, our study shows that lowering the film density can prompt earlier splashing.

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