Effect of Rotor Shielding on Fan-Outlet Guide Vanes Broadband Noise Prediction

Abstract

An analytical model for the rotor–stator broadband noise is improved by accounting for the rotor acoustic shielding. Both the analytical models for the stator broadband noise and for the rotor scattering are strip-theory approaches based on previously published formulations of the three-dimensional unsteady blade loading for a rectilinear cascade. Specific treatment is introduced to address the behavior around the cut on frequency of the duct modes both in the noise generation and in the noise scattering. A simple effect of the swirl between the rotor and the stator is considered using a Doppler shift in frequency. The power spectral density of the acoustic power and the sound pressure level at the duct wall are studied for the NASA source diagnostic test fan rig. The separate effects of the shielding by a cascade of the rotation of the rotor and of the swirl are investigated. Corotating modes dominate in the inlet. The rotor shielding decreases the acoustic power at intermediate frequencies but increases it at higher frequencies because of the frequency scattering and of the scattering in radial mode orders, which does not exist in a fully rectilinear model. The swirl has a strong effect that must be included.