Airfoil chord4/19/2023 For isolated airfoils or flat plates, these modifications basically consist of leading-edge serrations, comblike structures, and the application of flow-permeable or porous materials. With the aim of reducing the turbulence interaction noise, different leading-edge modifications have been developed in the past that affect the aerodynamic and acoustic properties of the airfoil. Whereas airfoil self-noise is the dominant source of noise in uniform and nonturbulent inflow conditions, turbulence interaction noise occurs due to the interaction of a turbulent inflow with the airfoil leading edge and strongly depends on the corresponding turbulence parameters. T he main aerodynamic sound generation mechanisms of airfoils are airfoil self-noise (boundary-layer noise, boundary-layer separation noise, trailing-edge noise, and tip noise) as well as turbulence interaction noise (leading-edge noise). At the same time, the porous modifications can reduce the aerodynamic performance, and hence the fan efficiency. It was found that a notable broadband noise reduction can be transferred from airfoil applications to the sound spectra of axial fans. In a third step, a possible transfer of the observed noise emission from airfoils with permeable leading edge to that of fan blades was investigated. With the aim of reducing turbulence interaction noise of axial fans, the fans were examined with regard to their aerodynamic and acoustic properties under grid-generated turbulent inflow conditions. Based on the results from that study, unskewed fan blades with four different permeable leading-edge designs were manufactured in a second step. This consisted of detailed aerodynamic and aeroacoustic measurements on 16 airfoils with different permeable leading-edge designs that were performed for various flow speeds and geometric angles of attack. In a first step, a wind-tunnel study was carried out. The airfoils and fan blades with permeable leading edges were made of an aluminum alloy using a powder bed fusion-based additive manufacturing process. A detailed experimental study on the aerodynamic performance and noise emission of airfoils and fan blades with permeable leading edges under disturbed inflow conditions was performed.
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