Design and manufacturing of aeroacoustic metamaterial: Textured rotor blades with enhanced acoustic and aerodynamic performance

Unmanned aerial vehicles (UAVs), commonly referred to as drones, have attracted increasing attention as urban aerial mobility platforms. A pivotal consideration in their optimization is the reduction of rotor blade noise without compromising aerodynamic performance. This study endeavors to advance the field by developing aeroacoustic metamaterials tailored specifically for rotor blades, to concurrently achieve noise reduction and thrust enhancement. To enhance these acoustic and aerodynamic performances, the surface of the rotor blade was designed to incorporate various texture patterns. These textured blades were fabricated using photopolymerization-type additive manufacturing. Experimental investigations revealed that the grid-textured blade exhibited superior efficiency in noise reduction but an inferior thrust force. Numerical simulations were conducted to investigate the effect of surface texturing on the airflow near the blade. These simulations revealed that surface texturing effectively diminished the turbulence kinetic energy in the proximity of the blade, resulting in a corresponding reduction in the noise levels. However, a patterned groove located at the leading edge induces flow separation, leading to a discernible reduction in the thrust. An adaptive texture gradation method was then employed to avoid flow separation at the leading edge, and the resulting grid-textured blade demonstrated reduced noise and augmented thrust. The simultaneous enhancement of acoustic and aerodynamic performances signifies the emergence of an aeroacoustic metamaterial, offering a promising solution to the critical challenge of noise mitigation without compromising propulsion efficiency.