Numerical analysis of the porpoising motion of a blended wing body aircraft during ditching

Abstract

The ditching performance of a BWB aircraft is studied using the numerical method. The unsteady Reynolds-Averaged Navier-Stokes equations and the Realizable k−ε turbulence model are solved by the finite volume method, the implicit volume-of-fluid model is adopted to capture the water-air interface, the six-degree-of-freedom model is employed to couple fluid dynamics and aircraft rigid-body kinematics, and the global moving mesh is used to deal with the relative motion between the aircraft and the water. The accuracy of the present numerical method is validated by the high-speed ditching experiment of a 3D flat plate. The porpoising motion of the BWB aircraft during ditching is discovered for the first time, and this motion is independent of the initial pitch angle, i.e., the amplitude and period of the motion and load curves are coincident for different initial angles. The porpoising motion is determined by a couple of hydrodynamic and aerodynamic loads, and the total load peak is mainly caused by the former. The hydrodynamic load is mainly from the staggered positive-negative pressure stripe on the aircraft belly. The variation in aerodynamic load is mainly induced by the compression work in the dynamic ground effect.