农药液滴撞击移动液膜和非对称冠状水花形成机理分析

Clarifying the impact law of pesticide droplets on the surface of plants is of great significance for improving the efficiency of pesticide spraying and pest control. A numerical model of the horizontal liquid moving liquid film with single droplet impinging was established by the method of coupled level set and volume of fluid. The motion characteristics and dynamic mechanism of the liquid droplet impacting the moving liquid film was studied, by analyzing the pressure distribution, velocity distribution and vortices cloud map inside the liquid after impact, the mechanism of kinematic discontinuity, jet flow formation and jet top-end splash were verified, and the asymmetric crown formation mechanism was revealed, it had guiding significance to explore the effective deposition and loss law of pesticide spraying. It can be seen that the flow of liquid film caused crown showed obvious asymmetric characteristics, such as the development of the upstream and downstream jets flow were inconsistent, uneven crown base thickness and different splashing degree at the end of jet flow on both sides, the crown base migrated with the flow of the liquid film, under the influence of the flow inertia of the liquid film, when the dimensionless velocity U was 0.8 and the dimensionless time T was 3.47, the crown base completely migrated to the right of the impact point; the neck pressure difference mechanism led to the formation of jet flow, and the development of the jet flow was determined by the radial movement of the droplet and the vortex at the end of the jet flow, with the increase of liquid film velocity(U is 0~0.8), the jet flow in the upstream grown rapidly along the horizontal direction, while the jet flow in the downstream tended to extend vertically upward, and the end velocity of the jet flow on both sides was increased; the velocity difference between the radial movement velocity and spreading velocity determined the splashing state at the end of the jet flow, the flow direction of the upstream liquid film was opposite to the spreading direction of the droplet, therefore the splash behavior at the upstream end was more significant than that at downstream.