Aeroacoustics of Jet-Surface Interaction and Passive Solutions for Mitigating Jet-Installation Noise

Aircraft noise levels have been significantly reducedwith the introduction of high-bypass ratio turbofan engines, particularly jet noise due to turbulence mixing. This, however, has led to engines with larger diameters and a closer coupling between them and the airframe. As a result, interactions between the exhaust jet flow and the wing give rise to an acoustic source known as jet-installation noise. In more detail, this source is generated by the impingement of unsteady pressure waves from the jet mixing-layer on the airframe surfaces and their scattering as noise at the wing trailing edge. Jet-installation noise becomes relevant particularly during take-off and approach conditions since the deployed flaps are located closer to the turbulent jet flow. Therefore, this thesis aims to elucidate the physical mechanisms behind jet-installation noise, followed by the development of passive mitigation solutions based on porous material technology and acoustic liners. A study on their effects and working mechanisms is performed, as well as on their feasibility from the aerodynamic perspective.