The Acoustic Analogy as a Tool of Computational Aeroacoustics

Abstract

The acoustic analogy proposed by Lighthill in 1952 in his jet noise theory provides an exact governing equation of noise generation away from the flow region. The generalization of Lighthill’s equation in the presence of moving surfaces by Ffowcs Williams and Hawkings in 1969 was a major advance. The primary impact of the governing equation of noise generation known as the Ffowcs Williams-Hawkings (FW-H) equation has been in the prediction of the noise of rotating blades such as high speed propellers and helicopter rotors. Since the mid-seventies many researchers have derived solutions to the FW-H equation in both the time and frequency domains. Sophisticated computer codes for noise prediction based upon the acoustic analogy have been developed with highly realistic blade geometry, kinematics and aerodynamic input. As a result of the demand by aeroacousticians, much effort has gone into the development of high resolution aerodynamics for use in acoustic codes. The acoustic analogy is now in a mature stage. The aircraft industry is beginning to rely on codes based on the acoustic analogy to control aircraft propulsion system noise. In this paper, we argue that, because of the exact nature of the FW-H equation, the availability of high quality aerodynamic data, sophisticated acoustic codes and high performance computers, the acoustic analogy is an important and useful tool of computational aeroacoustics. Some examples for advanced propellers and rotors are presented.KeywordsAircraft NoiseHelicopter RotorNoise PredictionAcoustic AnalogyAerodynamic DataThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.