Large eddy simulation of propeller–ground interaction effects on unsteady wake characteristics

Urban air mobility (UAM) vehicles are gaining considerable attention because of their potential to transform future transportation systems. When a propeller operates near the ground, its wake impinges on the ground, creating complex flow structures. These interactions influence aerodynamic performance, acoustic emission, and unsteady blade loading. Therefore, this study investigated the aerodynamics and aeroacoustics of propeller–ground interactions through experimental measurements and numerical simulations. A twisted two-bladed rotor was used as the reference configuration for both approaches. Large eddy simulation (LES) was conducted to investigate the effects of rotor-ground distance on wake development and turbulent flow characteristics at four clearance ratios, defined as the ratio of rotor height above the ground to the rotor radius: 0.3, 1, 2, and 3. The computed pressure coefficients obtained from LES were validated against experimental data across all clearance ratios. The results revealed that propeller–ground distance significantly affects wake evolution and flow dynamics. At various clearance ratios, the tip vortex impingement location shifts and the tip jet flow becomes stronger, producing pronounced upwash and downwash regions beneath the rotor. These flow features substantially alter the near-field pressure distribution and enhance unsteady flow fluctuations. Additionally, far-field acoustic measurements indicated that noise level increases as the propeller approaches the ground, although the magnitude depends on the observer angle. Spectral analysis confirmed that the elevated noise is predominantly broadband in nature, with noticeable amplification at the blade passing frequencies.