Control strategies for aircraft airframe noise reduction

 With the development of low-noise aircraft engine, airframe noise now represents a major noise source during the commercial aircraft's approach to landing phase. Noise control efforts have therefore been extensively focused on the airframe noise problems in order to further reduce aircraft overall noise. In this review, various control methods explored in the last decades for noise reduction on airframe components including high-lift devices and landing gears are summarized. We introduce recent major achievements in airframe noise reduction with passive control methods such as fairings, deceleration plates, splitter plates, acoustic liners, slat cove cover and side-edge replacements, and then discuss the potential and control mechanism of some promising active flow control strategies for airframe noise reduction, such as plasma technique and air blowing/suction devices. Based on the knowledge gained throughout the extensively noise control testing, a few design concepts on the landing gear, high-lift devices and whole aircraft are provided for advanced aircraft low-noise design. Finally, discussions and suggestions are given for future research on airframe noise reduction.