CFD simulation and measurement of the downwash airflow of a quadrotor plant protection UAV during operation

Abstract

To improve the effectiveness of unmanned aerial vehicle (UAV) spray, it is necessary to clarify the flow characteristics and penetration inside the canopy of the downwash airflow of UAV. This study used a three-dimensional computational fluid dynamic (CFD) model for the flow characteristics and velocity distribution of the downwash airflow generated by a quadrotor plant protection UAV at different flight velocities (1 ∼ 5 m/s) was established. The measurement tests for airflow velocity distribution inside the canopies were conducted. The results indicated that the spiral vortices appeared below the rotors and then evolved into inclined horseshoe vortices. The horseshoe vortices at the flight velocity of 5 m/s exceeded the flight height of the UAV and tended to cause droplet drift. When the flight velocity was larger than 4 m/s, it was difficult for the horseshoe vortex to enter the bottom of the canopy, which was not conducive to improving the droplet penetration performance. The diffusion and attenuation of the horseshoe vortex during the flow process led to an increase and then a decrease in the velocity distribution area in the Z-direction of airflow. In order to improve the droplet penetration performance, the optimal operating distance range between UAV and canopy was given when the flight velocity was less than 3 m/s based on the variation law of the velocity distribution in the Z-direction. The validation results showed that the simulated and measured values maintained the same trend.