Multisection approach for the vertical water impact of a fuselage

Although aircraft ditching is a rare event in the aeronautical field, it needs to be considered in the design phase to guarantee safety and ensure the certifications' respect. Besides experimental tests and high-fidelity approaches, the use of fast and efficient solvers, albeit of lower fidelity, is of primary interest to aircraft manufacturers to have a quick but at the same time accurate estimate of the hydrodynamic loads acting on the aircraft, to be effectively exploited in its conceptual and preliminary design phases. This is particularly true during the aircraft optimization process where many different configurations have to be analyzed. In this perspective, fully non-linear potential flow models, although remaining low fidelity approaches but being fully non-linear, provide accurate details, like pressure distribution, and should allow capturing some hydrodynamics phenomena occurring in ditching problems like cavitation and ventilation. An idea should be developing a 2D+t procedure which exploits a 2D fully non-linear potential flow model to describe the hydrodynamics of the aircraft ditching phenomenon. The 2D+t approach is based on a slender body approximation and reduces the 3D problem into a series of 2D cross section problems, with the shape of the section changing in time, in an earth-fixed frame of reference. As a first step through the implementation of a 2D+t approach, this paper presents a multisection procedure for computing the vertical water impact of a fuselage. Differently from the 2D+t method, in the multisection procedure the forward velocity in the longitudinal direction is not considered and the shape of the 2D sections don't change in time during the immersion. The proposed multisection procedure is based upon a 2D fully non linear potential flow hybrid BEM-FEM solver proposed in. The hybrid BEM-FEM approach has shown in the past good capabilities in describing the hydrodynamics of 2D water impact problems both in water entry with constant velocity and in the combined water entry/exit with varying speed. The numerical investigation aims to preliminarily verify the procedure here proposed through its application to a guided drop test of a scaled fuselage.