State-Space Inflow Model Identification from Viscous Vortex Particle Method for Advanced Rotorcraft Configurations

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This paper describes the methodology that identifies a state-space rotor induced inflow model from first-principle based viscous Vortex Particle Method (VPM) simulation for flight dynamics and control applications. Modern advanced rotorcraft configurations usually involve multiple rotors (e.g., co-axial), fans, wings, etc. where the aerodynamic interaction can be significant under certain flight conditions. The paper presents a unified state-space inflow formulation that addresses the aerodynamic interaction that is well suited for flight dynamics analysis and control design applications. In implementation, the unified inflow model is derived through system identification using VPM simulation generated data. The usage of first-principle based VPM provides a solid approach in capturing important rotor wake physics. This includes both the wake distortion and wake diffusion that are essential for an accurate interactional wake solution, without relying on empirical modeling parameters (e.g., vortex core size and wake dissipation parameters, etc.). The methodology of inflow model identification was first validated with a single rotor where measured data are available. Good agreement of the identified model response with the measurements was obtained. The methodology was further evaluated with a co-axial rotor system. Excellent correlation of the identified model with original VPM simulation was also obtained in both hover and forward flight.