Space Shuttle Rudder
Source: New Scientist
Airbus noted a recently filed US patent regarding the Space Shuttle's rudder, which splits to present two large area surfaces, used as air brakes to slow the vehicle. Suggesting this could have airliner application it could reduce need to deploy air brakes with their tonal (vortex) noise generation when heard on the ground.
By carving serrations into trailing edges, vortex generation thus noise would also be minimised. Also, no loss of lift would arise as is presently the case for conventional wing mounted brakes, so less engine power would be required on approach with even more noise reduction opportunity. The use of serrations to spoil flow causes the generation of eddy currents; these are more disorganised than air currents produced from a straight edge, which reduce pressure difference which reduces noise.
The concept of serrated wing and blade edges to mitigate tonal noise generation has wide potential to mitigate noise generation from a vast range of sources.