Numerical Analysis of Multirotor Aerodynamic Interactions in Forward and Transition Flight

The growing demand for urban air mobility (UAM) has accelerated the development of hybrid/electric vertical takeoff and landing (H-/eVTOL) aircraft, which use distributed propulsion systems that generate complex aerodynamic interactions during forward and transition flight. This study investigates the aerodynamic interactions between two propellers arranged in a one-after-another (OAA) configuration, using unsteady Reynolds-averaged Navier–Stokes (URANS) simulations coupled with the [Formula: see text] shear stress transport (SST) turbulence model. The numerical setup was validated against experimental data for the isolated propeller across all investigated advance ratios, showing good agreement. Results reveal that, in forward flight, the rear propeller experiences up to 24% thrust and 20% power loss due to the disturbed airflow created by the wake of the front propeller. This is accompanied by only a 21% increase in axial velocity at the rear propeller location, indicating less effective energy transfer and lower thrust. Pressure coefficient analysis at the rear propeller midspan within the overlap region indicates increased flow separation and lower local loading. During transition, the overlap decreases with tilt, yet at 30° and 60°, the rear propeller still loses up to 11% thrust and 10% power due to slipstream deflection. As the propeller tilt angle increases, the thrust in the propeller axis direction also increases; however, this requires more power and generates a more complex slipstream. These findings provide valuable insights into wake interactions and their influence on rear propeller performance, offering practical design guidelines to improve the efficiency and reliability of UAM vehicles.