An experimental investigation of pressure fluctuations in three-dimensional turbulent boundary layers

This dissertation presents experimental measurements and analysis of the surface pressure fluctuations beneath several turbulent boundary layers of practical interest. Pressure fluctuations in turbulent boundary layers are a source of noise and vibration that can accelerate structural fatigue. Pressure fluctuations and their correlation with velocity fluctuations is an important diffusive mechanism of turbulence transport. The approach was to study the statistics of both the surface pressure and the velocity field through new measurements of the fluctuating surface pressure and existing measurements of the velocity field and the covariance of the surface pressure and fluctuating velocity components.; Measurements were made in three types of flows. The first type of flow was a zero pressure gradient, two-dimensional, turbulent boundary layer ( Re_&thetas; = 7300 and Re_&thetas; = 23400). The second type of flow was a three-dimensional, pressure-driven, turbulent boundary layer that forms away from a wing-body junction. The third type of flow was the separating flow about the leeside of a 6:1 prolate spheroid at angle of attack. Measurements were made at two angles of attack, α = 10° and α = 20°, and two axial locations, x/ L = 0.600 and x/L = 0.772, in this type of flow.; Spectral scaling is discussed and various scaling combinations of the spectral power density of surface pressure fluctuations beneath two-dimensional boundary layers that cover a wide range of Reynolds number (1400 < Re_&thetas; < 23400) are presented. The nearly constant spectral levels are due to a lack of overlapping frequency structure between the large-scale motions and the viscous-dominated motions since each of these types of motion may have different flow histories due to the three-dimensional flow structure. This effect amplifies the importance of the middle frequency range to p′ as compared to two-dimensional flows.; The lack of similarity in the shape of the spectral power density preclude a direct extension of “universal” generalizations that are true for surface pressure fluctuations beneath two-dimensional boundary layers.; Measurements of the correlation coefficient between surface pressure and velocity fluctuations show that there can be sources of p away from the wall in three-dimensional flows. Sources of p away from the wall are significant in terms of fluid-structure interaction since they contribute low frequency fluctuations. (Abstract shortened by UMI.)...