ACTIVE RESONATORS FOR CONTROL OF MULTIPLE SPINNING MODES IN AN AXIAL FLOW FAN INLET

A research program was undertaken to explore the potential and practicality of developing active control Helmholtz resonators to attenuate excessive turbofan engine noise. The active Helmholtz resonator provides increased acoustic bandwidth by adding a controlled velocity via a secondary sound source. Plane wave tests demonstrated that the concept could be used both the increase a resonator’s absorption bandwidth and induct insertion loss bandwidth. For effective absorption of sound in a two dimensional duct environment, the active resonator concept was combined with a unidirectional radiation technique, which was extended to provide simultaneous suppression of multiple azimuthal, multiple radial and multiple blade-pass harmonic sound fields. The program culminated in a demonstration in the ANCF at NASA Glenn Research Center