The Control of Interior Cabin Noise Due to a Turbulent Boundary Layer Noise Excitation Using Smart Foam Elements

Abstract

In this work, the potential for a smart foam actuator in controlling interior cabin noise due to a turbulent boundary layer excitation has been experimentally demonstrated. A smart foam actuator is a device comprised of sound absorbing foam with an embedded distributed piezoelectric layer (PVDF) designed to operate over a broad range of frequencies. The acoustic foam acts as a passive absorber and targets the high frequency content, while the PVDF serves as the active component and is used to overcome the limitations of the acoustic foam at low frequencies. The fuselage skin of an aircraft was represented by an experimental test panel in an anechoic box mounted to the side of a wind tunnel. The rig was used to simulate turbulent boundary layer noise transmission into and aircraft cabin. An active noise control (ANC) methodology was employed by covering the test panel with the smart foam actuators and driving them to generate a secondary sound field. This secondary sound field, when superimposed with the panel radiation, resulted in a reduction in overall sound in the anechoic box. An adaptive feedforward filtered-x Least-Mean-Squared (LMS) control algorithm was used to drive the smart foam actuators to reduce the sound pressure levels at an array of microphones. Accelerometers measured the response of the test panel and were used as the reference signal for the feedforward algorithm. A detailed summary of the smart foam actuator control performance is presented for two separate low speed wind tunnel facilities with speeds of Mach 0.1 and Mach 0.2 and a single high speed tunnel facility operating at Mach 0.8 and Mach 2.5.