Numerical study of droplet impingement and spreading on a moving surface

The formation of an asymmetric lamella when a drop impacts a moving surface has been observed, but the underlying mechanism is not fully understood. In this study, we implemented a coupled level-set and volume-of-fluid method to simulate the asymmetric spreading of a drop on a moving surface. The dynamic contact angle model was used, with the capillary number calculated from the relative velocity at the contact line. The numerical method was validated with experimental data from the literature, and the spreading dynamics were also analyzed. The results indicate that the current method yields accurate predictions for lamella spreading, with a relative error in lamella width of less than 5%. This study reveals that the moving surface affects the spreading through the shear stress transferred from the surface to the liquid and the translation motion of the surface. Shear stress causes the lamella to either stretch or squeeze and the translation motion of the surface results in the advancing and receding phases existing together. These mechanisms lead to asymmetric spreading, and the asymmetricity of the lamella increases with the surface velocity and liquid viscosity. When the surface velocity is small, the effect of shear stress and translational motion only causes a translation of the lamella with no asymmetric spreading.