Internal-external flow transition effects on multibody separation dynamics of folding-wing UAVs: A coupled CFD-MBD approach

To address the coupled problem of sequential multi-UAV slide-out separation inside a payload cabin and rapid post-release wing deployment of folding-wing UAVs, this paper develops a multibody-dynamics framework based on Kane’s method and couples it with a six-degree-of-freedom (6DOF) solver and an unstructured dynamic-mesh CFD approach. The complete deployment process, from cabin exit to rapid wing unfolding, is analyzed with emphasis on three challenges: (1) high-dimensional dynamic coupling among multiple UAVs and hinged folding-wing mechanisms, (2) strong nonlinear aerodynamic interference, including flow separation, wake asymmetry, and vortex shedding during the transition from the internal cabin flow to the external flow field, and (3) numerical accuracy and stability under large-amplitude mesh deformation with multiple moving bodies. Results for a representative staggered-release configuration with a fixed interval of 0.6 s show reduced mutual wake interference and improved attitude stability during sequential separation. During the early internal-external transition stage, however, the reduced-order theoretical model deviates from the high-fidelity CFD–6DOF solution because of pronounced nonlinear separation, asymmetric wake development, and neglected lateral-directional coupling. The present results should therefore be interpreted as a feasibility demonstration for one representative release configuration rather than as a global optimization of the release strategy. Within this scope, the study provides a practical methodological basis and useful engineering guidance for the design of folding-wing UAV deployment schemes.