An Experimental Investigation of Pressure Fluctuations in Three-Dimensional Turbulent Boundary Layers
Technical rept. 16 May 1994-15 Dec 1999
VIRGINIA POLYTECHNIC INST AND STATE UNIV BLACKSBURG DEPT OF AEROSPACE AND OCEAN ENGINEERING
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Experimental surface pressure fluctuations measurements over a wide range of Reynolds number 1400Re0 23000 are presented for 3 types of turbulent boundary layers 1 a zero pressure gradient 2-D turbulent boundary layer, 2 a 3-D pressure-driven turbulent boundary layer that forms away from a wing-body junction, and 3 the separating flow about the leeside of a 61 prolate spheroid at angle of attack. The statistics of the fluctuating surface pressure and existing measurements of the velocity field and the covariance of the surface pressure and fluctuating velocity components were studied. The spectral power density of surface pressure fluctuations beneath highly three-dimensional flow contain nearly constant spectral levels within a middle to high frequency range, due to a lack of overlapping frequency structure between the large-scale motions and the viscous-dominated motions. Each of these types of motion have different flow histories due to the three-dimensional flow structure. The resulting RMS surface pressure fluctuation distributions reflect the importance of the high frequency wall region contributions. Scaling parameters for the spectra beneath three-dimensional flows must incorporate local flow structure in order to be successful. An analysis based on the Poisson equation shows that the variation of the high frequency spectral levels is related to the variation of near-wall mean velocity gradients and v structure. In the 61 prolate spheroid flow, near regions of crossflow Separation there is a local minimum in RMS surface pressure fluctuations, whereas around reattachments and under the large shed vortices there is a local maximum in RMS surface pressure fluctuations.
- Fluid Mechanics