RECENT STUDIES OF ROTORCRAFT BLADE-VORTEX INTERACTION NOISE

Recent results are presented from several research efforts aimed at th e understanding of rotorcraft blade-vortex interaction (BVI) in terms of the noise generation, directivity, and control. The results are bas ed on work performed by NASA Langley Research Center researchers, both alone and in collaboration with other research organizations. Based o n analysis of a simplified physical model, the critical parameters con trolling BVI noise generation have been identified. The detailed mappi ng of the acoustic radiation field of a model rotor in a wind tunnel h as revealed the extreme sensitivity of directivity to rotor advance ra tio and disk attitude. The control and reduction of BVI noise through the use of higher harmonic pitch control is discussed.