Stereo-PIV Study of Drone Propeller Wakes for Noise Reduction

The aerodynamic wake of small UAV propellers plays a central role in both thrust generation and noise emission, yet the flow mechanisms linking propeller geometry to tonal and broadband noise are still not fully understood. In this study, stereoscopic particle image velocimetry (stereo-PIV) is used to investigate the three-component wake flow of several drone-scale propeller concepts in hover, with simultaneous thrust, RPM, and acoustic measurements performed in an anechoic chamber. A commercial 16×5.4 T-Motor propeller is compared with a high-fidelity 3D-printed replica, a trailing-edge serrated blade, a trailing-edge flocked blade, an asymmetric three-blade rotor, and two toroidal closed-loop designs. All configurations are evaluated at a constant thrust of 5 N to ensure a consistent aerodynamic-acoustic comparison. The stereo-PIV measurements reveal clear geometry-dependent differences in wake coherence, tipvortex formation, and turbulence intensity. The baseline propeller produces a narrow, symmetric wake with strong coherent tip vortices, whereas the 3D-printed replica shows earlier vortex breakdown and enhanced small-scale fluctuations. Serrated trailing edges introduce only minor wake diffusion, while the flocked trailing edge causes severe separation and reduced propulsive efficiency. The asymmetric three-blade design weakens blade-passing tonal content by redistributing aerodynamic loading, producing a less periodic wake. The toroidal propellers suppress distinct tip-vortex cores and generate lower overall sound pressure levels, with the tri-loop configuration showing the most collimated and coherent wake structure. These results demonstrate how stereo- PIV can directly relate wake topology to acoustic behavior and provide flow-based guidance for the design of quieter UAV propellers.