Numerical study on the spread characteristics of raindrops impacting surfaces of different roughness levels
Abstract
The wing surfaces of aircraft generally have microscopic rough structures caused by processing and ice accumulation evolution, which significantly alter the spreading, wetting, and splashing behaviors after water droplets impact, and thereby affect the distribution of water collection coefficients on the wing surface and the ice formation patterns. Based on the Smooth Particle Hydrodynamics (SPH) method, this study constructs a triangular micro-rough wall - raindrop - gas-phase multiphase coupled numerical model, and conducts simulation experiments under three sets of working conditions: 0 m/s, 10 m/s, and 50 m/s lateral inflow velocities. It fully captures the dynamic evolution laws of the entire process of raindrop impact on the rough wing surface. The results show that without inflow, the raindrop spreads axially symmetrically, and the triangular rough structure is bound by the geometric pinning effect to retain the liquid phase, without fragmentation and splashing; at low inflow velocities, the shear force is introduced, and the symmetry of the liquid droplet spreading is broken, the liquid phase is infiltrated to the multiple levels of rough grooves, only weakening the droplet retraction effect, and the liquid droplet remains continuous and intact; when the inflow velocity increases to 50 m/s, the strong shear force exceeds the surface tension constraint threshold, and the liquid droplet’s downstream edge tears and generates a large number of secondary splashing small droplets, and the pinning and constraining effect of the rough structure fails. There exists a critical threshold for the inflow velocity. In the low-speed range, the rough structure can regulate the distribution of the liquid film, while in the high-speed range, it induces large-scale fragmentation and diffusion of water droplets. The research results can provide a refined mechanism basis for the numerical prediction correction of ice formation on rough wing surfaces and the optimization design of passive anti-icing structures for aircraft.