Acoustics of a Mixed Porosity Felt Airfoil
NAVAL UNDERSEA WARFARE CENTER DIV NEWPORT RI NEWPORT United States
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Lifting surfaces produce noise in operation, and porous materials have been shown to reduce this noise. Acoustic measurements were made on three arrangements of poroelastic material full-chord porosity, full-chord impermeability, and mixed porosity. A scaling scheme is presented that collapses the spectra acquired at different Reynolds numbers. The results are compared to applicable published data. The noise reduction produced by the mixed porosity arrangement is found to be similar to the fully-porous arrangement at low Reynolds numbers. The noise reduction produced by the mixed and fully-porous foils does not match over the entire frequency range at higher Reynolds numbers.
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