Airfoil-gust interactions in transonic flow

Leading edge noise is a significant broadband noise source in aircraft engines, and is the primary broadband noise mechanism in outlet guide vane noise in turbofans, and broadband rotor wake interaction noise in contra-rotating open rotor engines. Previous authors have studied the effects of various aspects relating to this noise source, including airfoil geometry effects, cascade effects, and Mach number effects. However, previous literature has not addressed the effects on the noise due to locally supersonic regions that might be present in the mean flow around the rotor blades. The current work uses computational aeroacoustic methods to investigate the effects of locally supersonic regions on the noise due to airfoil- gust interactions. An established computational aeroacoustics code has been extended to give stable predictions in supersonic regions with a localized artificial diffusivity method. Initial results of a NACA 0012 airfoil in M = 0.8 flow interacting with oncoming vortical waves are shown, alongside results for a NACA 0006 airfoil in M = 0.5 flow at a 6° angle of attack. The changes to the noise and the underlying mechanisms are discussed for both cases, including additional noise sources caused by the supersonic region.