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Drop impact-freezing on an incline is omnipresent in nature and industrial applications like 3D (three-dimensional) printing, but most current research concentrates on the impact instead of the interaction between impact and freezing. This paper thus developed an OpenMP-paralleled phase field model to probe into the underlying physics in 3D printing conditions. The finite difference solution to the Cahn–Hilliard equation helps track the evolving liquid–gas interface, and the liquid fraction is defined over the whole computational domain to distinguish between solid and fluid. The model was first validated against two experiments, showing agreeable consistency. Then, it was applied to inclined impact without and with phase change. The effect of inclination angles was also examined. It was found that increasing inclination angles can extend contact time, and that solidification cannot retard the gravity-driven fluid flow down the incline at an inclination angle of 45° but can at an inclination angle below 30°. Besides, the retracting speed declines with increased inclination angles. [ABSTRACT FROM AUTHOR]

Drop impact dynamics with solidification has been a hot topic of research recently. However, numerical studies to that end mainly concentrate on spherical drops, paying less attention to non-spherical ones that are ubiquitous in industrial applications like additive manufacturing and plasma spraying. Therefore, a phase field model accelerated with the shared-memory parallelism OpenMP is proposed to simulate the impact of a non-spherical heavy metal droplet in actual additive manufacturing conditions. The tracking of the gas–liquid interface is realized by the finite difference solution of the Navier–Stokes equation and the Cahn–Hilliard equation. We use the liquid fraction defined all over the computational domain to distinguish between solid and fluid. The model was then employed to predict the impact and freezing dynamics of non-spherical droplets, with the focus on the effects of the aspect ratio, of the contact angle, and of the phase field mobility. It shows that the established model could well capture the axis switching process, that rebounding accompanying the axis switching process could be hindered by solidification, and that larger phase field mobility could smooth drop profile, rendering it round in the axis switching process. [ABSTRACT FROM AUTHOR]

A comprehensive numerical model has been developed, which is capable of predicting the spreading of a high-speed yttria-stabilized zirconia (YSZ) droplet with solidification microstructure formation under a horizontal electric field in plasma spraying processes. The numerical model entails the explicit finite difference solution of the Navier–Stokes equations and the energy balance equation, coupled with the Cahn–Hilliard equation to track the liquid–gas two-phase interface and with a phase field model for solidification microstructure formation involving polycrystalline growth. The electric force is added as a source term in the Navier–Stokes equations, and the fluids are assumed to be perfect dielectrics. The in-house code is written in Fortran and run in parallel. The results reveal that the retracting process could be completely inhibited using a horizontal electric field and that solidification time is greatly reduced. A new mechanism to suppress droplet breakup/splash could be realized, featuring reduction of the rising angle the spreading front makes with a substrate. All the cases show columnar grains within a splat. Besides, the model is validated against experimental results, with gratifying agreement achieved. [ABSTRACT FROM AUTHOR]

A novel numerical model was developed to investigate air entrapment in binary droplet impact with solidification microstructure formation under practical plasma spraying conditions. The evolving liquid–gas interface was tracked by the explicit finite difference solution to the Cahn–Hilliard equation, coupled with the Navier–Stokes equations. Another diffuse interface model was invoked to trace solid–liquid and grain–grain boundaries. The model was discretized using an explicit finite difference method on a half-staggered grid. The velocity pressure coupling was decoupled with the projection method. The in-house code was written in Fortran and was run with the aid of the shared memory parallelism, OpenMP. The time duration over which gas compressibility matters was estimated. Typical cases with air entrapment were studied with the model. The effect of droplet porosity on air entrapment was probed into as well: the larger the porosity of a droplet, the bigger the trapped air bubble. The grain growth near the air bubble is skewed. Moreover, a case without air entrapment was also shown herein to stress that air bubbles could be suppressed or even eliminated in plasma spraying by adjusting the landing positions of successive droplets. [ABSTRACT FROM AUTHOR]

A phase field model enhanced with the shared memory parallelism OpenMP was proposed, capable of modeling the impact of a heavy metal droplet under practical plasma spraying conditions. The finite difference solution of the Navier-Stokes equations, coupled with the Cahn-Hilliard equation, tracks the gas-liquid interface. The liquid fraction, defined over the computational domain, distinguishes fluid from solid. The model is employed for Ni and YSZ drop impacts after ruling out the effect of mesh size. The model exhibits a reasonable parallel-computing efficiency, and the predicted maximum spread factors agree well with analytical models. [ABSTRACT FROM AUTHOR]

• A free-energy-based surface tension model used in the conservative level set modeling. • Distinct impact regimes in 3D printing conditions considered. • Parallel computing based on OpenMP employed. The recently developed conservative level set method is second order in nature, thus making it amenable to explicit finite difference solutions in three dimensions. Due to a lack of efficient numerical models in simulating impact-freezing problems in 3D printing conditions, this paper puts forward a model based on the coupling of the conservative level set equation and the Navier-Stokes equations. The interfacial tension is represented by the free-energy-based model, which is free from the cumbersome computation of curvature that may induce parasitic flows. The model is further augmented with the thermal field to deal with phase change. The model is discretized on a half-staggered grid, is written in FORTRAN, and is accelerated with the shared-memory parallelism, OpenMP. Furthermore, a simple yet effective dynamic contact angle is applied. Three validation tests were conducted, corresponding to different impacting regimes. It shows that the model could well predict the full rebounding, and especially, the splashing occurring in drop impact onto solid surfaces. [Display omitted] [ABSTRACT FROM AUTHOR]