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

## TL;DR

This study examines how droplet impact on curved, vibrating leaves affects pesticide spray effectiveness, revealing how leaf curvature and vibration influence droplet spreading and splashing.

## Contribution

The study experimentally quantifies the combined effects of Weber number, leaf curvature, and vibration frequency on droplet impact dynamics, offering practical guidelines for pesticide application.

## Key findings

- Higher leaf curvature caused asymmetric droplet spreading with increased diameter along the x-axis and decreased along the y-axis.
- Droplet spreading duration decreased by 35.88% at high Weber numbers (≥ 168), while splashing probability increased.
- Resonance between droplet and leaf motion at 40–50 Hz maximized spreading and splashing risk.

## Abstract

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 (θp → 0) to counter-rotating (θp → 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.