Aircraft noise is an important topic of research, as researchers have been seeking ways to reduce it. The current thesis aims to advance the state of the art of airfoil trailingedge (TE) noise reduction, by experimentally testing numerically optimized TE designs studied by the author, and obtained from semi-empirical models prediction. Dierent congurations of a non-at plate, NACA-0012 airfoil, and at-plate trailing-edge serrations are investigated. A wind tunnel test section that provides the required environment is designed and created. The test section walls have been acoustically treated to simulate an acoustically far-eld environment with forwarding ight. The two sides of the wind tunnel test section are tted with anechoic chambers and lined with acoustic transparency tensioned cloth screens which act as an interface between the test section and the anechoic chambers to provide a smooth ow surface while eliminating the need for a jet catcher and reducing interference eects. Its aeroacoustic performance is measured. Results show that background noise is comparable with other aeroacoustic wind tunnels worldwide. A straight TE airfoil and at plate were tested as a benchmark, and then compared with serrated trailing-edge geometries. Results show that the serration geometry is eective in reducing noise and that noise radiated from the TE is at least 6 dB higher than the background noise, satisfying the requirements for aeroacoustic measurements.The ability of the trailing-edge serrations to reduce TE noise is examined through numerical optimization study. Three dierent serration geometries are optimized for the overall noise from 0.1 kHz to 10 kHz. The noise spectra was initially modeled using semi-empirical models by Howe, for a semi-innite at plate, at zero angle of attack and at low Mach numbers. The single-size sawtooth optimization study found the optimum performing TE sawtooth geometry (in terms of noise reduction), which was conrmed experimentally. The measurements conrmed that numerical optimization predicted a much larger noise reduction compared to measured values. Comparison of single-size sawtooth, slit and sinusoidal TE designs show that, while the three geometries reduced i I would like to greatly thank all people who either contributed to the work described with this thesis or to me personally during the working time on it. First and foremost, I would like to express my gratitude and appreciation to my supervisor professor Joana Rocha. Her continuous support and guidance have signicantly contributed to my research progress during my PhD.Without a scholarship from my home country Libya, it would have been dicult or impossible to achieve this work. I wish all progress and prosperity to my country and peace to all people.Many thanks to all friends for their emotional supports and invaluable advises. Their encouragement during more dicult phases of my study has inspired me and made me more productive.Finally, I dedicate this thesis to my family; my beloved mother and father whose love continues as long ...

This study presents an experimental study of the effect of sawtooth trailing-edge serrations on airfoil instability noise. The far-field noise measurements are obtained to investigate the noise radiation characteristics of a NACA-0012 airfoil operated at various angles of attack: 0°, 5°, and 10°, and covered Reynolds numbers of 2.87 × 105, 3.71 × 105, and 5 × 105. It is found that as the Reynolds number increases, the instability noise shifts from tonal to broadband, whereas as the angle of attack increases, it shifts from broadband to tonal. Furthermore, sawtooth trailing-edges are used to minimize instability tonal noise, leading to considerable self-noise reduction. Parametric studies of the serration amplitude 2 h and streamwise wavelength λ are performed to understand the effect of sawtooth trailing-edges on noise reduction. It is observed that the sound pressure reduction level is sensitive to both the amplitude and streamwise wavelength. Overall, the sawtooth trailing-edge with larger amplitude and smaller wavelength produce the greatest amount of noise reduction.

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