This article delves into the aeroacoustics of a forward-flight propeller ingesting small- and large-scale turbulent wakes, focusing on the distinct mechanisms of noise generation. The study aims to advance our understanding of turbulence ingestion noise mechanisms when turbulence with varying characteristics (intensity, coherence, and length scales) is ingested by the propeller, using numerical simulations. The research primarily focuses on turbulence ingestion, as it sets the structure of the unsteady loading that drives the sound field in urban environments. The authors explore how differences in inflow scale, coherence, and spatial extent modify the sectional unsteady loading and the corresponding far-field noise. They also investigate blade-level noise source decomposition and blade-to-blade correlation studies, coupled with modulation intensity analyses, to reveal two primary, yet distinct mechanisms in turbulence ingestion noise of a propeller in forward flight. The study employs a lattice-Boltzmann-based solver to investigate the flow and noise characteristics arising from a two-bladed propeller ingesting two distinct turbulent wakes, generated by upstream cylinders of different diameters. The findings provide a high-fidelity mechanistic comparison between two canonical ingestion regimes, which can be used in predictive models. The authors conclude by emphasizing the importance of turbulence characterisation in predicting propeller noise in complex inflow environments, and suggest future research directions to further develop predictive models for propeller–turbulence-ingestion noise.
