Active noise control with resonant flush-mounted piezoelectric cells in the presence of airflow: Wind tunnel experiments

Abstract

Methods and technologies to control the noise coming from turbulent flows impinging on outlet guide vanes in turbofan engines are tremendously needed nowadays to comply with new legislation on acoustic environment pollution. The following paper relies on preliminary research proposing a new experimental design of active noise control system to be further integrated into a jet engine outer guide vane prototype, consisting of multiple flush-mounted piezoelectric cells. Here, three active cells are placed on the bottom wall of a wind tunnel with upstream acoustic excitation generating grazing incident waves for different airflow velocities. Using a downstream microphone as an error sensor, the active system succeeds in improving the transmission loss of the sample by 2.5 dB at the target frequency (670 Hz) corresponding to the main piezo acoustic mode with airflow velocities up to 20 m.s−1. These early experimental results confirm the ability of the concept to interact with the ambient acoustics without disturbing the airflow as in passive solutions using porous materials, for instance, leading the path to future experiments with realistic turbulence generating acoustic sources on the leading edge of the vane profile.