Robust Control of Turbulent Boundary Layer Noise Transmission Through a Stiffened Panel

Turbulent boundary layer (TBL) induced noise is one of the dominant 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 transmission loss of CFRP panels they are equipped with active 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 TBL is tested at flow speeds up to Mach 0.16. The CFRP panel (500 x 800 mm^2) is stiffened with four stringers and equipped with five piezo-ceramic patch actuators and up to 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. Robust H∞ 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. By inclusion of additional performance outputs in form of laser scanning vibrometer (LSV) measurements it is possible to gain global vibration reduction and an enhanced radiation mode control. Algorithms for the identification of the generalized plant are additionally presented. Finally, an overview of the achieved results is given