Establishing universal scaling laws for pressure fluctuations in high Reynolds number rough wall turbulent boundary layers

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PI: Devenport, William JProposal Number: 1436088The goal of the proposed research is to investigate experimentally and theoretically the scaling of pressure fluctuations in high Reynolds number boundary layers over rough walls. The focus of the work will be on practically and scientifically-relevant conditions at which most vehicles operate and at which universal behaviors are most likely to be observed. Results from the proposed research could have a strong impact on engineering for prediction of sound and vibration produced by boundary layers, and on scientific understanding of pressure effects with the development of a predictive function for rough-wall boundary layer pressure spectra.The proposed work is based on recent findings that pressure fluctuations within turbulent boundary layers over rough surfaces behave differently that velocity fluctuations, and this different behavior is important. The PI proposes to conduct experiments in a rather unique facility at Virginia Tech to explore the wall-pressure spectrum and the turbulence scales that it reveals. Prior results indicate that there are three different scaling regions (low, medium and high frequency), and the proposed experiments aim to establish the persistence of these scalings, and the physical processes they imply, as the geometry and density of the roughness elements is varied. Proposed are also experiments on a two-scale surface that could lead to the development of an interpolation function for rough-wall boundary layer pressure spectra. The proposed work would be important for the theory of boundary layer turbulence with engineering applications where noise is a concern, such as vehicle design (cars, planes, helicopters) and wind turbines. The proposal also offers a plan to integrate research with education. High school, undergraduate and graduate students will be involved in designing and building parts of the wind tunnel as well as manufacturing of the new rough surfaces, providing a complete hands-on, engineering experience.