Computational aeroacoustic study of aircraft slat tracks and cut-outs

摘要

As one of the major contributors to aircraft noise, the noise generated by high-lift devices has been explored for many years. However, the noise related to the slat track system, which includes all the extrusive components connecting the slat and the main element, is still generally studied through experimentation due to the complex geometry. In this project, the aerodynamics and aeroacoustics of the slat track and cut-out, especially the main element cut-out, were investigated through numerical simulations for the first time. Two methods were employed in this work. Noise propagation is first studied via a compact source model to evaluate the contribution of each source individually and to investigate the influence of the slat track system on the noise propagation in the slat region. The APE-IV system was employed but modified by using a more accurate expression of enthalpy perturbation to calculate the acoustic fields. The results show that both the slat track system and the background flow modify the sound propagation path. The energy radiated towards the ground is increased due to the interaction of sound waves with the slat track system and the background flow. Detached eddy simulations were run to investigate the mechanisms of the slat track and cut-out noise generation. Major noise sources in the slat cove region are identified and a noise generation feedback loop is proposed. The results show that the increment of noise levels due to the existence of the slat track system is two-fold. The slat track and the cut-out generate noise individually and they also amplify the noise generated within the slat region when the sound waves propagate though the slat cove area and interact with the slat track and cut-out. The dominant frequencies of the spectrum are seen to shift towards the high frequencies due to these added on components. In this work, two kinds of possible noise attenuation approaches were proposed and studied. Geometries based on replacing the sharp cut-out on the main element leading edge with an edge-rounded or a sealed cut-out have been proved to be able to reduce the cut-out noise significantly. Application of acoustic bulk absorbing material can also attenuate the cut-out noise efficiently for a certain range of frequencies.