Tip vortex characteristics and aerodynamic–hydrodynamic analysis of aerial–aquatic cycloidal propellers

For an aerial–aquatic vehicle, the complex transmedia scenarios require higher maneuverability of the propeller system. As a vector propeller, the cycloidal propeller can easily change the thrust direction without significantly changing its configuration, which makes it a good candidate for an aerial–aquatic vehicle. Furthermore, the efficiency of the aerial–aquatic vehicle propeller is essential, and its design must balance the requirements for aerial and aquatic conditions. In this paper, a new metric Sη is defined to evaluate the propeller efficiency for aerial–aquatic conditions, and a study about the effects of several key geometric parameters was conducted. The hydrodynamic and aerodynamic characteristics were evaluated by computational fluid dynamics, and the simulation accuracy was validated against experimental data (the experimental data employed for hydrodynamic model validation are sourced from publicly available datasets, whereas the aerodynamic model validation utilizes in-house experimental results generated by our research team). After that, the analysis revealed congruent aerodynamic/hydrodynamic performance with similar Reynolds numbers. Therefore, we focus on analyzing its hydrodynamic performance. Critical geometric parameters—pitching axis position, pitching angle symmetry, blade thickness, and solidity—were systematically evaluated. Furthermore, geometric parameter modifications directly modulate the tip vortex core diameter and velocity magnitude generated by the cycloidal propeller.