Rotor Blade Tip Vortex Characterisation with Implications for Blade–Wake Interaction Noise

The development of low-noise rotor designs for electric vertical take-off and landing (eVTOL) aircraft has received growing attention in the context of urban air mobility, where noise is a critical factor for public acceptance and overall success. Rotor noise emission is closely tied to near-field rotor dynamics, particularly the formation of blade tip vortices and their subsequent interaction with following blades during the take-off and landing operation. While past studies have attempted to model tip vortices, most approaches are based on stationary blade configurations, which may not adequately capture the dynamics of vortices generated by rotating blades. As a result, the characterisation of rotor blade tip vortices remains a relatively underexplored research area. This study investigates the evolution of rotor blade tip vortices across wake age, with the objective of developing an in-depth understanding of their spatiotemporal development and spectral characteristics. Experimental characterisation of such vortices is extremely challenging, if not infeasible, owing to their transient, three-dimensional, and highly unsteady nature. Consequently, their dynamics have remained poorly resolved in prior research. Recent advances in scale-resolved, high-fidelity numerical methods, however, now enable detailed examination of these complex structures. By exploiting these capabilities, the present study offers one of the first comprehensive analyses of tip vortex from its origination, growth, and eventual impingement, thereby addressing a long-standing gap in rotorcraft aeroacoustics. A deeper physical understanding of rotor blade tip vortices directly supports the development of a higher-order polynomial representation of their turbulence spectra. As this expression will be employed to refine Glegg’s blade–wake interaction noise model, which currently relies on turbulence descriptions derived from stationary blade tip vortex shedding. Updating this framework with a more realistic representation of rotating blade tip vortex turbulence is essential for improving predictive accuracy and, ultimately, for achieving enhanced acoustic performance in urban air mobility applications.