Dynamics of Harmonic Active Sound Control with a Harmonic Acoustic Pneumatic Source

Abstract

During takeoff, the harmonic noise of the turbofan is the main acoustic nuisance for people near airports. Much research has been done on the topic of active reduction of turbofan noise. Loudspeakers used as secondary sources present the disadvantage of being fragile and need a high consumption to produce the required sound intensity. In this context, an alternative solution, called the Harmonic Acoustic Pneumatic Source (HAPS), has been designed to generate a high harmonic noise level controllable in amplitude, phase and frequency. Previous studies on the subject have demonstrated the possibility to perform active noise control with a ring of HAPS in a cylindrical duct, but the convergence time of the controller was about several seconds. The dynamics of the controller is thus the limiting factor for active noise control applications. The objective of this study is to address this problem by characterizing and designing a controller with a short response time, typically less than a second. Therefore, we present an experimental configuration with a loudspeaker acting as a primary source and a HAPS mounted laterally on a rectangular duct. A microphone is placed in acoustic near-field. The control strategy, based on integral feedback, aims at minimizing the pressure at the microphone location. Simulations are realized with a first order model for the HAPS and compared to the experimental results which include measurements of the HAPS response time and the controller response time for active noise reduction. This study is a first step to the objective of performing active noise control in presence of flow, with an experimental campaign planned on the MaineFlow duct (Le Mans, France). This work is supported by Association Nationale Recherche Technologie (ANRT, France) and Safran Nacelles (Le Havre, France). We gratefully acknowledge Marc Versaevel from Safran Nacelles.