Experimental Wind Tunnel Testing and Numerical Optimization Studies for Airfoil Trailing Edge Noise Reduction

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 trailing edge (TE) noise reduction, by experimentally testing numerically optimized TE designs studied by the author, and obtained from semi-empirical models prediction. Deferent configurations of a non-flat plate, NACA-0012 airfoil, and flat-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-field environment with forwarding flight. The two sides of the wind tunnel test section are fitted 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 flow surface while eliminating the need for a jet catcher and reducing interference effects. Its aeroacoustic performance is measured. Results show that background noise is comparable with other aeroacoustic wind tunnels worldwide. A straight TE airfoil and flat plate were tested as a benchmark, and then compared with serrated trailing-edge geometries. Results show that the serration geometry is effective 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 different 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-infinite flat 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 confirmed experimentally. The measurements confirmed 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 noise from a straight TE, sawtooth serrations result in larger noise reduction than single-size slit and sinusoidal………….