Study of airframe noise and its reduction for commercial aircraft

In the present paper the main mechanisms and basic characteristics of the airframe noise are analyzed. The airframe noise is produced by the pressure fluctuation of the flows around the landing gears and high lift systems. Aerodynamic noise from landing gears and leading edge slots are essential broadband noise, their strengths and the strength of broadband noise of flaps are varied with 6th, 4.5th and 5th power of flow velocity respectively. The existence of parasitic noise in flight must be concerned too. The noise reducing projects of QTD II, RAIN, SILENCE(R) and TIMPAN are discussed and their results are presented in the paper. The computational methods are briefly introduced. The goals of noise reduction for future commercial aircraft proposed by foreign countries are given, which indicates a huge challenge to the future commercial aircraft design.