The interaction of a standard boundary layer with a rough porous surface has been investigated experimentally. Comprehensive boundary layer and surface pressure measurements have been carried out using a long flat plate equipped with several streamwise and span-wise surface pressure transducers. To reveal the effects of the interaction of a boundary layer with a porous surface, three types of porous materials with different porosity and permeability constants are examined. Results have shown that porous surface treatments can significantly alter the boundary layer flow properties and cause significant changes to the energy cascade of the velocity fluctuations within the boundary layer. It has also been shown that porous surfaces cause a reduction in the high-frequency energy content of the surface pressure fluctuations. Moreover, it has been found that the use of a porous surface can lead to a significant reduction in the spanwise coherence and the length-scales of the boundary layer flow structures. The emergence of a strong hydrodynamic field inside the highly permeable surfaces has also been explored. The results presented in this paper are of great importance for the better understanding of the flow-porous interaction mechanisms and have demonstrated that our understanding of the problem is limited and more high-quality experiments are required for the development of bespoke passive porous-based flow and noise control techniques.
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