An Experimental Study on Aerodynamic Performance Degradation of a Drone Propeller due to Rainfall

This study presents a two-stage investigation to elucidate the performance degradation of a multirotor UAV drone in heavy rainfall scenarios. The first stage employed field tests on an autonomous UAV equipped with sensors for real-time communication during periods of intense thunderstorms and contrasting calm weather conditions. These in-situ measurements revealed a significant increase in power consumption for the drone during heavy rainfall. To isolate and understand the fundamental physical mechanisms affecting propeller performance in such conditions, the second stage focused on controlled laboratory experiments. A hovering 9.4-inch propeller operating at various rotational speeds was subjected to a range of simulated rainfall rates within a dedicated rain chamber at Iowa State University. Comprehensive force measurements were acquired under both dry and simulated rain conditions. High-speed photography provided detailed visualizations of water flow dynamics across the propeller surface, capturing the intricate phenomena of water runback. Furthermore, the experiment employed two sets of blades, one with a hydrophilic (enamel-baseline) surface representing a baseline configuration and the other coated with a superhydrophobic material (Neverwet coating by Rust-oleum) to explore potential performance enhancements. The behavior of the wake flow fields for dry propellers and those under rain was analyzed using Particle Image Velocimetry (PIV), revealing a reduction in wake velocity due to the simulated rainfall. Additionally, force measurements revealed a decrease in thrust production and an increase in motor power consumption during simulated rain events. These findings offer crucial insights to guide future efforts in multirotor UAV design and operation optimization for robust performance in wet weather conditions.