Numerical study of the discrete frequency noise generation in an axial flow fan

Abstract

Aeroacoustics was firstly established in order to describe the noise produced by aircrafts. The optimization of propulsion systems in airplane engines lead to an important reduction of jet noise but other acoustic effects, like fan noise, were still an issue to deal with. The knowledge of the sources and the behaviour of noise will allow the development of procedures or actions to reduce sound levels. One possibility is the establishment of a methodology based on numerical simulations to characterize the aerodynamic noise. Lighthill's analogy was generalized later by Ffowcs Williams and Hawkings to be applied to turbomachines. Following the analogy, this paper presents a numerical methodology focused on the study of the generation and propagation of the discrete frequency noise in the far field in an axial flow fan. A hybrid approximation was employed to separate the aerodynamic and acoustic problem. Also, experimental results are carried out to validate the numerical methodology.