Flowing characteristics of aluminum droplets impacting curved surface

Abstract

In order to reveal the mechanism of reaction between aluminum droplet and curved wall, a numerical calculation model based on the volume of fluid method of aluminum droplet impacting curved wall is established. By analyzing the influence law of Weber number, Ohnesorge number and wall curvature on the process of droplet impacting the wall, the spreading characteristics and flow mechanism of droplet on curved surface are studied. The results show that the flow characteristics of aluminum droplets after impacting the wall are affected not only by inertial force, surface tension, and viscous force, but also by the structure of the wall. The behavior patterns of the droplets contain adhesion, rebound and splash under different Weber numbers. Because energy dissipation is produced in both spreading process and retracting process, the retracting speed of droplet is always less than its spreading speed. During the flow of the droplet, there are two pressure peaks and velocity peaks at the contact point, while the two peaks appear respectively at the moment when the droplet impacts the wall and when the droplet is about to rebound. In the behavioral mode of rebound, as Ohnesorge number increases, the maximum spreading diameter of the droplet gradually decreases, and the contact time is shorter. In the behavioral mode of adhesion, the spreading radius of the droplets is of oscillatory decay. Within the same period, the maximum spreading coefficient of the larger-Ohnesorge number droplets is smaller, and the decay rate is faster and the oscillation period is shorter. With the increase of wall curvature, the maximum spreading coefficient of droplet increases and that on the plane is the minimum. Based on the calculation results, the empirical formula is revised. Compared with the previous formula, it can well predict the maximum spreading coefficient on the curved surface, whose average error is within 3%. Further, according to the conservation of energy, theoretical models which predict the maximum spreading coefficients when droplets impact a curved and plate wall are also established. Compared with the scenario on the plane, the spreading coefficient of droplet on the curved surface is related to not only the motion parameters of droplet and the wettability of wall surface, but also the ratio of wall curvature to droplet curvature. More importantly, the new theoretical model takes into account the coupling effects of Weber number, Reynolds number, curvature ratio and contact angle, so it has stronger applicability and better robustness. The research results in this work will provide the theoretical basis for practical engineering application.