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Unmanned aerial vehicles (UAVs) have become an important research topic due to their wide range of applications and potential to meet the future air transportation demands. In many configurations of UAVs, the rotors interact with the wake of upstream bodies, which is of pivotal importance to the aerodynamic and aeroacoustic performance. The studies of flow structures and noise sources for rotors interacting with adjacent upstream bodies at Reynolds numbers lower than 105, which is the operating condition of most small UAVs, are limited. In the current study, numerical simulations are conducted to investigate the interaction between a rotor and the wake of an airfoil at low Reynolds numbers around 104 using the Spalart–Allmaras delayed detached eddy simulation method and acoustic analogy based on Farassat's formulation 1 A. The results show that the axial forces and the surface pressure perturbations of the airfoil are closely coupled with the rotor rotation. The effect of interaction on the rotor blades depends on the relative angle of attack. Furthermore, an analysis of the surface pressure fluctuations corresponding to the noise sources shows that the tonal noise at the blade passing frequency and its harmonics is mainly caused by periodical interaction, and the high-frequency noise is produced by the shedding vortex at the trailing edge of the rotor. [ABSTRACT FROM AUTHOR]