There has been many research studies surrounding the propulsion and the landing gear noise reduction and many-advanced technology have been created regarding those subjects.
Airframe noise is mainly divided into two different types, Bluff body noise and the edge noise. The High lift devices noise falls into the edge noise, which is when turbulent flow passes an end of object or gaps in between the structures.
During the landing and take-off the two main aerodynamic noises comes from high lift devices and landing gears. The noises from high lift devices are mainly from slats, trailing edge and leading edge. Today there are some advanced computational software that could help reduce the airframe noise before the manufacturing stage, which would save both time and money.
Reducing airframe noise is one of the major research areas that the aircraft industry is investing in due to the importance of the noise on take-off and landing and the impact on the communities near the airport. Noise is generated on the airframe when the flow passes an object on an aircraft, such as; the landing gear or the wings.