Aerodynamic modeling and analysis of aerial-aquatic rotorcraft performance near and crossing the air-water interface

Blending the agility of aerial drones with the covert capabilities of underwater submersibles, the aerial-aquatic rotorcraft has garnered substantial interest due to their unparalleled capacity to traverse both air and water. Nevertheless, a critical hurdle for these vehicles lies in mitigating the adverse effects of repeatedly transitioning between these environments, particularly during water-surface takeoffs. Currently, research on the interference caused by rotors approaching water surfaces remains limited. This paper introduces a novel adaptive rotor aerodynamic model based on continuous finite vortex theory to predict rotor thrust within gas–liquid flow field. Initially, the model’s sensitivity to system parameters was analyzed to optimize its predictive capabilities. Subsequently, a comprehensive ground/water experimental setup was designed to investigate the intricate aerodynamic interactions between the rotor flow field and water. By varying rotor sizes, the characteristics of the rotor flow field and water surface were examined at different rotor-water surface distances. The performance of different modeling methods was analyzed based on the rotor experimental data of a diameter of 0.38 m, and the prediction results were quantified using the percentage of the mean-square error. The results show that the average error of the finite vortex rotor model is the smallest. Finally, a novel transition boundary is proposed to divide the rotor flow field of the gas–liquid mixture into two stages. The thrust loss zone is defined to delineate the safe operating range of the aircraft, providing a basis for the design of aerial-aquatic rotorcraft.