Measurements of the wavenumber-frequency spectrum of wall pressure fluctuations under turbulent flows

Abstract

The prediction of the vibratory response of structures excited by turbulent flows implies a good knowledge of both aerodynamic and acoustic components of the wall pressure fluctuations. In the present work, experiments were aimed at measuring wall pressure fluctuations under turbulent flows, in order to separate the two exciting loadings. The experiments were conducted in the anechoic wind tunnel of Ecole Centrale de Lyon (France). Two configurations were more precisely studied : a turbulent boundary layer and a cylindrical bar in crossflow. A rotative array has been designed that allows the measurement of a complete map of cross-power spectral densities over a large area. A post-processing has been developed to transform the space-frequency data into wavenumber-frequency spectra. Results for the boundary layer are consistent with the Corcos model. Analysis of the spectra shows the presence of an acoustic pressure field, which magnitude is about 5% of the aerodynamic pressure field. Concerning the bar, the whistling frequencies do appear on wavenumber spectra, but not the broadband acoustic field previously observed for the boundary layer. Besides, the strong flow inhomogeneity makes quality of wavenumber spectra worse.