Measurement, simulation and synthesis of turbulent-boundary-layer-induced vibrations of panel structures

Abstract

The characterization of the vibro-acoustic behavior of structures excited by a turbulent boundary layer (TBL) is an expensive task and thus raises the demand for less expensive alternative solu-tions. This contribution focuses on the synthesis of TBL-typical structural vibration by means of a loudspeaker array placed in front of a panel structure. The derived method can be applied to any flat or curved panel structure (e. g. an aircraft fuselage section). The work is subdivided into three main parts. Firstly, experiments in an aero-acoustic wind tunnel are performed to capture the characteristics of the TBL excitation and the induced vibrations of a rectangular aluminum plate. Secondly, a finite element model of the plate and a statistical excitation model are derived and validated with measurement data. Despite the use of simple simulation models, a high agreement between measurement and simulation is achieved. It is concluded that realistic values for the vibrations of panel structures can be derived. In the third part of this work, the aluminum plate is mounted in the test opening of a transmission loss facility. A loudspeaker array located in the reverberant sending room of the facility is placed in front of the panel and the frequency response functions (FRFs) from the loudspeaker array to the structural vibration of the plate are derived. The structural vibration is measured with a scanning laser Doppler vibrometer placed in the semi-anechoic receiving room of the facility. The filtering of the simulated target values through the inverse FRFs yields the required control signals for the loudspeaker array. Twelve loudspeakers, corresponding to 60 loudspeakers per square meter, are used to synthesize the TBL-induced structural vibration up to 500 Hz. The synthesized structural vibration is consistent with the target values obtained from simulation.