![]() Airframe noises mainly include leading edge slat noises and trailing edge flap noises. Therefore, airframe noises become the bottleneck for overall noise reduction of an aircraft, where it should draw more and more attention in aircraft noise researches. Especially when an aircraft enters the site, the engine stays at an idle power state, and the airframe noise has become the main source of aircraft noises. The noise level of engines has been reduced obviously and controlled effectively. Compared with turbine noises, jet noises are gradually decreased. With the increase of bypass ratio of turbofan engines, the exhaust velocity of engines has been decreased. To reduce jet noises, engine noises can be reduced through increasing bypass ratio and slowing down jet velocity. As a result, the higher jet velocity is, and the louder jet noises will be. ![]() In addition, jet noises are in direct proportion to the 8th power of its jet velocity. Therefore, periodic rotating turbine in the engine and the periodic interference will cause typical discrete noises. ![]() Turbofan engines are a typical rotary machine. Usually, fan noises and jet noises are the main noise sources of an engine. Regarding engine noises, contemporary civil aircrafts widely apply turbofan engines. Airframe noises are mainly the sum of aerodynamic noises and mechanical noises caused by the pressure fluctuation. Keywords: aerodynamic noise, high-lift airfoil, FW-H method, LES.Īerodynamic noises generated by aircrafts are divided into two parts including engine noises and airframe noises. For both of them, the sound pressure levels reached the maximum value in the direction perpendicular to the chord line. Acoustic directivity of leading edge slats and trailing edge flaps showed an obvious dipole characteristic. Computational results show that: the leading edge slats generated aerodynamic noises mainly because of the unsteady waves which were caused by the grooves between the slat and main wing, as well as small wake eddies generated on the trailing edge of slats flaps generated aerodynamic noises mainly because of mixing between high-frequency small-scale eddies and low-frequency large-scale eddies caused by flow separation around the wing flaps. Finally, based on the verified numerical model, contribution amounts made by each high-lift airfoil component to noises as well as major factors affecting aerodynamic noises were analyzed. ![]() Results show that: the numerical computation method used in this paper can provide an accurate solution for computing far-field aerodynamic noises. The numerical computation method was verified by experiments. The integration method FW-H (Ffowcs Williams-Hawkings) was used to compute far-field noises. Unsteady flow field data on the solid wall face was extracted as the noise source. In this paper, LES (Large Eddy Simulation) was used to conduct numerical simulation of flow fields of three-dimensional high-lift L1T2 airfoil. In numerical computation of aerodynamic noises, the solution accuracy of flow fields has an obvious impact on detailed computation of eddy turbulence and acoustic results.
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