Integration of a State-Space Viscous Vortex Particle Method within Flight Dynamics Simulations

This paper presents the integration of a state-space viscous vortex particle method (SS-VVPM) into rotorcraft flight dynamics simulations. More specifically, the near wake is modeled using a near-wake vortex-lattice method, while the far wake is represented by viscous vortex particles. The VVPM equations are formulated as a nonlinear, time-varying system in first-order form, allowing the wake dynamics to augment those of the rigid body and rotors. This formulation enables the coupled vehicle, rotor, and wake dynamics to be trimmed and linearized for use in stability analysis and flight control design. Different strategies for coupling the near wake to the particle wake are investigated, and a tip-edge shedding approach is identified as the best compromise between computational cost and accuracy. Verification is carried out for a generic utility-helicopter rotor in hover and forward flight through comparisons with previously validated free-vortex wake methods. Results show good agreement in wake geometry, thrust prediction, and tip-vortex trajectories, indicating that the particle-based formulation retains the dominant wake physics of the legacy model. Additional simulations for generic helicopter, tiltrotor, and electric vertical takeoff and landing (eVTOL) configurations over a range of flight speeds further demonstrate that the method reproduces the expected changes in wake structure from hover to forward flight.