Reduction of Flap Side Edge Noise by Active Flow Control

Abstract

One dominant airframe noise source is situated at the side edge of the extended wing flap. The objective of the present study is to reduce this noise by blowing air into the flap side-edge vortex to displace or destroy the vortical structure and thus reduce the emission of sound. PIV measurements without blowing yield a rather complicated unsteady vortical structure at the flap side-edge which confirms the assumption of a noise source. This is verified by microphone array measurements. They show that the flap side-edge noise, besides other noise sources, is present over a broad frequency range. The flight parameters such as angle of incidence and slat and flap angles, however, determine which noise source is dominant. PIV measurements with blowing show that the vortical structure can be almost completely dispersed and that the maximum vorticity in the vortex core is reduced. Consequently, a reduction of the flap side‐edge noise can be seen in the microphone array measurement. In addition, the sound pressure level in the acoustic far field is reduced by 3 to 4 dB above 1.25 kHz.