Infinite Beamforming: Wavenumber Decomposition of Surface Pressure Fluctuations

Abstract

The fluctuating pressure field underneath a turbulent boundary layer can lead to excitation of the surface structure of airplanes, trains and cars. At high flow speeds, this excitation becomes a major noise source in the vehicle interior. In the past, the characteristics of this excitation have been measured by the DLR in wind tunnels and in flight tests. A beam forming technique using planar waves was used as wavenumber decomposition in order to analyze the pressure fluctuations present over an installed microphone array. The information contained in the wavenumber spectrum resulting from the analysis is essential when empirically modeling the excitation behavior of a surface exposed to a pressure field. Speed, direction, and propagation mechanism (acoustic or hydrodynamic) of pressure waves can be determined from the position of sources in the wavenumber domain. This makes the wavenumber decomposition a helpful tool for the characterization of source mechanisms. In this paper, a summary of the test results is given. The attributes and potential of the wavenumber decomposition are emphasized in particular.