Study on the Characteristics of UAV Propeller Blade-tip Vortex Based on Background Oriented Schlieren

Propeller blade-tip vortex interference is an important cause of UAV noise. Measuring the generation and evolution process of the blade-tip vortex structure is key to reveal the noise generation mechanism. Focusing on the flow field characteristics of UAV propellers, a blade-tip vortex measurement method based on Background Oriented Schlieren (BOS) was developed. This method has advantages such as simple system structure, convenient installation and debugging, and the ability to obtain quantitative density field distributions. Ground tests were conducted on the propeller of a domestic UAV to measure the dynamic development process of the axial flow field structure. The experimental results show that after the blade-tip vortex detaches from the tip, it moves away from the blade and towards the rotation axis. The larger the rotational speed, the larger the radius of the blade-tip vortex and the faster its movement speed. Vortex trails form on both sides of the blades, and as the rotational speed increases, the range of these trailing structures expands. When the pitch angle increases, the interference of the blades on the flow field becomes more significant, and the non-uniformity of the flow field density distribution intensifies. These research results will provide technical support for studying the noise generation mechanism of propellers and designing noise reduction solutions for UAVs.