The Aeroacoustics of Helicopter Rotors - Lessons Learned from Wind Tunnel Tests (Invited Keynote Paper)

Abstract

This paper discusses the aeroacoustics of helicopter rotors on the basis of results from recent rotor model testing in acoustic wind tunnels and illustrates how this knowledge is utilized to both improve theoretical prediction capabilities and provide guidance towards the design (and operation) of acoustically less intrusive helicopters. To this end the current understanding of discrete frequency and broadband rotor noise generation and radiation is described for a number of important operational conditions both in terms of the farfield acoustic propagation and of the underlying source mechanisms. The use of wind tunnel experimental results in furthering theoretical approaches to predict rotor noise are briefly discussed. Efforts towards rotor noise reduction are treated and an outlook is given on promising areas of further rotor noise research.