Unsteady flow simulation of a variable-sweep morphing aircraft coupled with flight control system

Abstract

Morphing aircraft has adjustable aerodynamic shapes and is suitable for variable flight conditions. And there have been growing interests in recent years. However, the forces and moments are highly nonlinear, bringing challenges in design and modeling of flight control system (FCS). In this paper, unsteady Computational Fluid Dynamics (CFD) simulations are performed by solving the Arbitrary Lagrangian–Eulerian (ALE) governing equations on unstructured dynamic mesh, then unsteady aerodynamic characteristics of a variable-sweep morphing aircraft at hypersonic speed are acquired. The nonlinearity index theory is employed to analyze the nonlinearity of pitching moments. FCS is designed using nonlinear dynamic inversion control, taking attitude angles and sweep angle into consideration. Unsteady flow simulation is performed using unsteady CFD coupled with FCS. Cases of open and close loop morphing flight over the variation of sweep angle corresponding to flight conditions are studied. Results show that the nonlinearity of unsteady forces and moments are significant. The combination of unsteady CFD and FCS provides a powerful approach to the study of morphing aircraft.