Active Reduction of Turbulent Boundary Layer Induced Noise

Abstract

The turbulent boundary layer (TBL) 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. Increasing the transmission loss of CFRP panels, they can be equipped with active structural acoustic control (ASAC) systems. These systems consist of a control unit and surface mounted actuators and sensors. Structural vibrations of the panel are measured by the sensors and filtered by the control unit to estimate the radiated sound power in the far field. The transfer path from actuators over the structure to the sensors is called the controlled plant. Based on this information and a mathematical model of the controlled plant, the controller calculates the signals for the actuators in order to reduce the noise radiation.