Experimental investigation of droplet impact behavior considering leaf curvature and vibration effects

The impact behavior of droplets on crop leaves is a key factor in evaluating pesticide spray effectiveness. However, the coupled influences of the Weber number (We), leaf curvature (C^*), and leaf vibration frequency (f) on droplet impact dynamics remain insufficiently understood.

By independently regulating We, C^*, and f and using high-speed imaging, we found that higher leaf curvature caused asymmetric spreading, with the maximum diameter increasing by 6.89% along the x-axis and decreasing by 1.95% along the y-axis. At high We (≥ 168), spreading duration was reduced by at least 35.88%, while splashing probability increased. Vibration experiments showed that droplet-leaf motion shifted from synchronous (θ_p → 0) to counter-rotating (θ_p → π) as f increased from 10 to 80 Hz. Within the resonance range (40-50 Hz), both spreading and amplitude reached peak values, accompanied by the highest splashing risk. A quadratic regression model developed from a three-factor orthogonal design identified We and f as the dominant factors influencing maximum spreading (P < 0.05; We > f > C^*).

This study clarifies the coupled roles of We, C^*, and f in droplet-leaf interactions and suggests maintaining We < 132 in practical spraying. Under typical conditions, droplet impact velocity should be kept at 3-5 m/s, and reduced to 2-3 m/s for larger droplets (> 500 μm). To avoid resonance-induced splashing, airflow in air-assisted spraying should be controlled at 6-10 m/s. These findings provide guidance for improving pesticide deposition and optimizing spray practices.