Behaviors of fan tone noise under the influence of circumferentially non-uniform steady pressure perturbation

Abstract

The purpose of this study is to investigate the fan tone noise behavior under the influence of circumferentially non-uniform steady pressure perturbations caused by the engine pylon/bifurcation. The paper presents theoretical study with experimental and computational approaches on the noise of fan stages with and without a downstream cylinder which simulates the presence of the engine pylon/bifurcation, and further, describes comprehensive assessment of the fan tone noise behaviors. Firstly, model fan test results in an anechoic test facility for far-field noise and sound pressure spectra in the duct ahead of fan blades are presented to investigate the influences of the pressure perturbation. Secondly, the pressure fields ahead of blades obtained from three-dimensional unsteady CFD using UPACS are given for better understanding of phenomena affecting the fan tone noise. Finally, a new theory for fan noise prediction is developed to take into account the potential disturbance from the pylon, which interacts with the rotating rotor blades. Quantitative comparisons between the prediction and the experiment under different conditions of the pressure perturbation are presented.