Numerical Investigation of Aerodynamic Interactions in a Twin-Propeller Compound Helicopter

High-speed compound helicopters surpass the forward-speed limits of conventional helicopters and expand the flight envelope, yet close multi-component integration induces complex aerodynamic interference, whose underlying mechanisms and evolution with flight speed must be understood to support integrated aerodynamic design. This study examines the principal aerodynamic interactions in a box-wing, twin-propeller compound helicopter at flight speeds of 30–110 m/s. Time-accurate Reynolds-averaged Navier-Stokes calculations with dynamic overset grids are performed for isolated-component, rotor-airframe, rotor-propeller, and complete configurations. At 30 m/s, direct impingement of the main-rotor wake produces highly non-uniform propeller inflow, pronounced periodic propeller-thrust fluctuations, and substantial lift losses on the advancing-side wing panels. As flight speed increases, the wake is convected downstream and direct interference weakens, although lateral asymmetry persists. When the airframe is included, the lateral propeller thrust-coefficient trend observed in the rotor-propeller configuration is reversed, while box-wing lift is redistributed unevenly among the individual panels. At 90 and 110 m/s, the main-rotor thrust-coefficient ranges in the complete configuration lie entirely below the corresponding isolated-rotor ranges. These findings clarify how flight speed and component integration jointly govern complete-configuration aerodynamics, providing a basis for reliable aerodynamic assessment and configuration optimization of high-speed compound helicopters.