Aerodynamic noise analysis of tilting rotor in edgewise flow conditions

Abstract

This paper presents a comprehensive experimental analysis of the noise characteristics of an isolated tilt-rotor system under edgewise flight conditions. The investigation explores the effect of rotor tilt on noise and aerodynamics using flow velocity, thrust, and far-field noise measurements. Flow field results show that as the tilting angles vary, there is a change in speed over the rotor blade surface, which influences vortex formation and wake attributes. The far-field noise spectra revealed a significant decrease in sound pressure level with increasing tilt angle, predominantly evident in both the high-amplitude tonal peaks and the broadband signal within the low-to-mid frequency range. The directivity patterns of the overall sound pressure level also demonstrated a reduction in magnitude with the tilting of the rotor. This reduction was observed consistently across all top-plane observation points, with a monopole directivity trend. Meanwhile, in the side plane array, the decrease was primarily evident above the plane of rotation with a dipole directivity pattern. The radiation direction at which the minimum sound pressure level occurs was identified near the rotation plane, irrespective of the tilt angle. Furthermore, the time-dependent noise analyses revealed dominant and persistent signal characteristics at the blade passing frequency, whereas the mid-frequency range exhibited more intermittent behaviour, and the high-frequency range indicated transient characteristics.