Integrated Multibody–CFD Analysis of Low-Speed Separation and Folding-Wing Deployment for UAV Swarms Released from High-Altitude Payload Bays

Rapid deployment of folding-wing UAV swarms from high-altitude payload bays is strategic, but low-speed separation and wing unfolding are complicated by wake interference and nonlinear aerodynamic coupling. This work presents an integrated multibody–CFD framework coupling a six-DOF Kane-based dynamics model with high-fidelity CFD/6-DOF simulation. Unstructured dynamic meshes and UDFs update real-time attitudes, while an aerodynamic database parameterized by angle of attack, sideslip, and deployment angle supplies nonlinear force/moment coefficients. Validation with four 20 kg UAVs released at 2000 m and 25 m/s, each completing a 90^∘ wing deployment in 0.2 s, shows agreement with CFD within 5% in vertical translation and pitch, but reveals up to 0.03 m lateral drift and 3^∘ roll from asymmetric vortices. The lift coefficient rises from near zero to about 0.5, with a pitching-moment minimum at γ≈50^∘, confirming strong nonlinearity. The framework captures key longitudinal dynamics and indicates the need for enriched lateral aerodynamic data to refine separation strategies and attitude-control laws for swarm payload-bay release.