Experimental characterization of the turbulent boundary layer over a flat plate

Pressure fluctuations within a Turbulent Boundary Layer (TBL), which inevitably develops over a body immersed in a flow field, induce noise either by energizing the solid surface or with a direct contribution. The attenuation of this source of noise is particularly critical in aircraft and automotive industry, considering the increase of traffic and the extension of urban areas together with the rising public health concern. For this reason, the physical understanding of noise production and attenuation is becoming increasingly important in such engineering fields. Studies devoted to understand the characteristics of the Wall-Pressure Spectra (WPS) in a TBL have been conducted over the years, leading to a development of statistical models for the wall-pressure fluctuations. Such models are commonly used as input for the determination of the structural response of the wall and the noise prediction in many engineering applications. However, they are heavily dependent upon empirical quantities, thus they can be tuned and improved basing on experimental databases for different flow conditions. An experimental characterization of the turbulent boundary layer over a flat plate under zero pressure gradient has therefore been conducted in the present work. The aim of this project is to study the trend of the WPS in a turbulent boundary layer, in order to improve the physical understanding of the interaction between the grazing flow and the solid surface, and enrich the existing database in literature to promote the improvement of statistical models. Experiments have been carried out in the WAABLIEF (Wind tunnel for the Aerodynamic and Acoustic study of Boundary Layers Including pressure gradient EFfects) facility at the von Karman Institute for Fluid Dynamics (VKI) in Rhode-Saint-Genèse, Belgium. The experimental campaign includes velocity and wall-pressure measurements by means of hot-wire anemometry and microphone-array measurements, respectively. Moreover, an innovative procedure for the calibration of the microphone array is proposed in this study. In addition, preliminary Particle Image Velocimetry (PIV) measurements have been conducted, in order to explore the possibility of using such a technique to provide additional information on the velocity field in the TBL over the flat plate. In conclusion, the results obtained in this work constitute an extended database for velocity and pressure fields that offer the opportunity to validate and improve the statistical models available in literature.