Numerical simulation of airflow field from a six–rotor plant protection drone using lattice Boltzmann method

Rotor unmanned aerial vehicles (UAVs) for pesticide spraying have been widely used in China during the past three years. In order to improve the effectiveness of pesticide application and reduce environmental risk caused by spray drift, it is important to clarify the spatiotemporal distribution characteristics of airflow field of the drone. The airflow field produced by the UAV plays a key role in droplets delivery during the spraying. In this study, the lattice Boltzmann method (LBM) based on a mesoscopic kinetic model was used to simulate the airflow field of a six–rotor plant protection drone. The airflow field of drone in hover and at varied flight speeds (1.0–5.0 m s−1) and various altitudes (1.5–3.5 m) was investigated. The characteristics of airflow separation, airflow coverage equivalent area and “steep” effect were investigated numerically. The peak value of vertical downward velocity (V–Y) on the detection surface was analysed. Results indicate that the flight speed and altitude had a significant effect on the distribution of the airflow field. The predicted values in the vertical direction using the average velocity attenuation model (Y–DAVA) corresponded well with experimental measurements. The wake of airflow field had a significant backward tilt when the drone was flying forwards, thus when the flight speed was 4.0 m s−1 and 5.0 m s−1, the wake of the airflow field lifted off the ground, whereas the transverse separation appeared as horseshoe vortices. For flight speeds of 3.0 m s−1 and an altitude of 3.0 m the distribution of V–Y was the most uniform.