Propeller-noise reduction by microfiber coating on a blade surface

Abstract

The popularity of small aerial vehicles has dramatically increased in recent years and propeller noise from such vehicles is a public health concern. Further advancement and utilization of small aerial vehicles require a substantial focus on noise reduction. Microstructures using surface and coating technology are applied in a variety of ways to address this engineering challenge. This study investigates a microfiber coating as a passive means for reducing propeller noise. The microfiber coating is comprised of a fibrous structure and has been previously shown to be a passive mean for reducing drag on a circular cylinder. To begin testing the efficacy of the microfiber coating for propeller noise reduction, microfiber-coated strips are placed at different spanwise locations on propeller blades. The sound pressure level produced by the rotating propeller is measured using a sound-level meter. The microfiber-coated propeller exhibited a lower sound pressure level than that of the uncoated propeller. At a Reynolds number of 7.4 × 104 based on the chord at the 75% spanwise station of the propeller blade, the microfiber-coated propeller achieved a noise reduction of up to 1.6 dBA compared to that of the uncoated propeller. The microfiber coating is effective in reducing broadband noise associated with the interaction of the vortex shedding associated with laminar boundary layer separation. It is found that the noise-reduction performance is a function of the spanwise location of the microfiber-coated strips.