TABLE OF CONTENTS Roland Ewert and Eric Manoha
The applications described in Sections 6.5.2 and 6.5.3 address the general context of the numerical prediction of the aerodynamic noise generated by aircraft in the vicinity of urban airports. It is known that, for the largest existing and future aircraft, the noise radiated in the approach phase is evenly generated by the engines (working at reduced thrust) and the airframe. Airframe noise sources are known to be mainly located in landing gears and in high-lift devices, slats, and flaps, which are deployed during the approach.
Among all the complex noise-source mechanisms associated with high-lift devices, trailing-edge noise has probably received the most extensive attention (mostly theoretical and experimental) and is a perfect candidate for the evaluation of the emerging CAA techniques of numerical simulation based on LES. The trailing-edge noise mechanism is associated with the acoustic scattering of the airfoil turbulent boundary layer convected at the trailing edge. In this process, the quadmpolar (acoustically inefficient) nature of the convected eddies is transformed into dipolar sources, which are much more acoustically efficient.
The numerical simulation of the complete problem, including the local noise-source simulation and the far-field noise radiation, faces the difficulty of handling fluctuations covering a very extended range of length scales and amplitudes: turbulent eddies that generate noise have small lengh scales but high energy, whereas the acoustic waves radiated away have comparatively very long wavelengths but small amplitude. Thus, trailing-edge...
