Self active cancellation of fan noise

Abstract

Reduction of fan noise is an important problem in the successful deployment of drones and UAV's. This paper considers a new approach to reducing fan and propeller noise based upon micro vibrations of the propeller blades around their axis of support. Experimental testing was carried out on a five bladed fan arrangement. The micro fan blade vibrations are induced with a pitch link actuator arrangement driven by an electromagnetic actuator. When used in conjunction with a digital feedforward active noise controller, the micro blade vibrations were found to provide global attenuations of fan radiated sound the order of 5 to 10dB of the first few fan tones. The level of required vibrations and the associated electrical power required for the cancelling micro vibrations was shown to be very small compared to the fan motor power requirements. The results demonstrate that the innovative approach, termed “self active cancellation of fan noise”, has good potential for global reduction of fan and propeller noise.