Reduction of Turbulent Boundary Layer Noise with Actively Controlled Carbon Fiber Reinforced Plastic Panels

Abstract

The turbulent boundary layer (TBL) is one of the dominant external noise sources in high subsonic aircrafts. Especially in modern aircrafts where common materials for fuselages are currently substituted by carbon-fiber-reinforced-plastics (CFRP), it is essential to avoid a decrease of passenger comfort as a result of an inferior transmission loss of the new materials. To increase the transmission loss of CFRP panels they are equipped with active noise reduction systems. In this paper the results of an experimental study in the aeroacoustic wind tunnel of the German Aerospace Center (DLR) are presented. An active panel excited by a TBL is tested at flow speeds up to Mach 0.16. The CFRP panel (500 x 800 x 2.7 mm^3) is equipped with five piezo-ceramic patch actuators and ten accelerometers. Active structural acoustic control (ASAC) and active vibration control (AVC) are used to reduce the broadband TBL noise transmission in the bandwidth from 1 to 500 Hz. Feedforward and feedback control algorithms are applied in the experiments and show high performance even in presence of plant uncertainties. To improve control results the generalized plant framework of robust control is utilized for global feedback control. Finally, an overview of the achieved results is given.