Noise reduction design and analysis on flap side-edge shape modification

Flap side-edge noise is a significant noise source for airplane at takeoff and landing stages. The noise generation mechanism from flap side-edge noise is analyzed by numerical simulation of unsteady flow field using Very Large Eddy Simulation (VLES). Two kinds of flap side-edge shape modifications are proposed on the basis, and their frequency spectrum and directivity of far-field noise are compared with the baseline configuration using permeable integral surface Ffowcs Williams and Hawkings (FW-H) acoustic analogy method to investigate their effects on noise reduction. Via the numerical simulation of flow field and acoustic field, it proves that the flap side-edge noise is broadband noise in nature. The different shapes of flap side-edge change the pattern of flow field, vortex structures and the developing process of vortex, thus having influences on noise source distributions and characteristics of far-field noise. The result shows that at the given 5° angle of attack, the proposed flap side-edge shape modifications can achieve reduction of the overall sound pressure level (OASPL) ranging from 1 to 2 dB without decreasing the lift and drag aerodynamic performances too mach.