Comments On The Aeroacoustics Of Helicopter Rotors

Helicopter rotor aeroacoustics has been an active area of research in the past twenty years. Theoretical analysis together with much experimental work have helped in today's understanding of the many mechanisms responsible for rotor noise generation. Helicopter rotor noise prediction has turned out to be a tougher problem than turbofan and advanced propeller noise prediction . The reason is the multitude of noise generating mechanisms in rotors producing both the discrete and broadband noise. The following comments are a theoretian's view of the state of the art of rotor aeroacoustics. Much broader views were expressed in the two excellent papers of A. R. George [1, 2]. In particular, George's interesting analysis of the state of our understanding of various rotor noise mechanisms [2] is very relevant to present author's comments. Furthermore, a paper presented in this meeting by Farassat and Brentner [3] explains some of the ideas and opinions expressed here in more details.