Effects of different cross-flow fans on the hovering aerodynamic characteristics of a propulsive wing

The multi-axis propulsive wing aircraft is a novel type of electric vertical takeoff and landing (eVTOL) vehicle that achieves both VTOL and forward flight by tilting its propulsive wings to alter the direction of aerodynamic forces. However, during hover, the propulsive wings are less efficient than rotors, resulting in significant energy consumption. The number of blades in the cross-flow fan is a critical parameter affecting the efficiency of the propulsive wings, as well as their aerodynamic forces and wake characteristics. To enhance the hover performance of propulsive wings, a numerical study was conducted using unsteady Reynolds-averaged Navier–Stokes equations and sliding mesh technology to investigate the impact of blade number on aerodynamic characteristics during hover. The effects of blade number on the aerodynamic forces and efficiency of the propulsive wing were analyzed, and the flow field and wake characteristics were compared across different stages. Additionally, an aerodynamic test platform was developed to measure the thrust of the propulsive wing at various rotational speeds. The reliability of the numerical method was validated through comparisons between numerical and experimental results. The results indicate that the aerodynamic forces, efficiency, flow field velocity, and turbulent kinetic energy of the propulsive wings are highly sensitive to blade number. However, this sensitivity is non-monotonic, exhibiting an initial increase followed by a decrease. Specifically, the aerodynamic force of the propulsive wings increases by up to 78 %, while the power load improves by a maximum of 15 %, significantly enhancing load capacity and energy utilization efficiency. This progression can be divided into distinct phases, each meeting different design objectives, such as optimizing for high aerodynamic force or high efficiency. As the blade number increases, interference between the airflow and blade vortices gradually diminishes, strengthening the wake structure and reducing fluctuations in aerodynamic forces. However, when the blade number exceeds 28, a decline in aerodynamic force amplitude is observed, with a maximum reduction of 19.5 %. Additionally, due to the wake structure, the turbulent kinetic energy of the propulsive wings exhibits a banded distribution, with higher values in the positive vortex regions, approximately 23 % greater than those in the negative vortex regions.