Effects of hub wake and engine exhaust on pusher propeller aerodynamics in a compound coaxial helicopter using high-fidelity LBM simulation

Abstract

Coaxial compound helicopters with aft-mounted pusher propellers offer extended range and high-speed capability but are highly sensitive to complex wake interactions. During high-speed forward flight, unsteady and asymmetric wakes generated by the upper and lower hub fairings, mast fairing, and engine cowling are convected along the tail boom and impinge on the pusher propeller. The inflow entering the propeller disk is decelerated and distorted, which increases the effective blade angle of attack and causes variations in thrust, torque, and overall propulsive efficiency. Herein, the unsteady aerodynamics of a full-configuration coaxial compound helicopter based on the Sikorsky-Boeing SB>1 Defiant, modeled without main rotor blades, are analyzed using PowerFLOW, a high-fidelity solver based on the lattice Boltzmann method. Simulations capture the evolution of fuselage-hub wake structures, their interaction with the pusher propeller, and resulting changes in aerodynamic performance. Results indicate that wake impingement reduces propeller thrust and efficiency compared with the isolated propeller and induces azimuthal thrust asymmetry owing to local inflow distortion and partial blade stall. The findings provide a detailed understanding of how decelerated and distorted inflow affects pusher propeller performance, offering guidance for aerodynamic optimization and vibration mitigation in next-generation high-speed coaxial compound helicopters.