Study on flowing characteristics of aluminum droplets impacting on a curved surface

In order to reveal the mechanism of reaction between aluminum droplet and curved wall, a numerical calculation model based on VOF method of aluminum droplet impacting curved wall was established. By analyzing the influence law of Weber number, Ohnesorge number and wall curvature on the process of droplet impacting on the wall, the spreading characteristics and flow mechanism of droplet on curved surface were studied. The results show that the flow characteristics of aluminum droplets after collision with 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 number. Because energy dissipation is produced in both spreading and retracting processes, 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 oscillating attenuation. 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. Comparing with the previous formula, it can better predict the maximum spreading coefficient on the curved surface, which average error is within 3%. Further, according to the conservation of energy, theoretical models which predicts the maximum spreading coefficient when droplets impact on a curve and plate wall are also established. Compared with the plane, the spreading coefficient of droplet on the curved surface is not only related to the motion parameters of droplet and the wettability of wall surface, but also related to 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 more stronger applicability and better robustness. The research results of this paper will provide the theoretical basis for practical engineering application.