Numerical Simulation of Ditching of a Twin-Fuselage Aircraft

doi:10.12382/bgxb.2022.0111

Abstract

Abstract:

Aircraft ditching is a trans-media process, namely the process of the aircraft going from air to water. The exploration of the physical phenomena and dynamic characteristics of trans-media objects can provide insights into the research on airplane ditching and water entry of trans-media vehicles. The ditching process of a twin-fuselage aircraft is studied. The unsteady Reynolds-averaged Navier-Stokes (URANS) method, VOF method, dynamic grid technique and 6DOF model are used to numerically simulate the ditching process. Based on the numerical validation of the 3D plate water-skipping experiment, the effect of pitch angle on the ditching process of the twin-fuselage aircraft is analyzed. The numerical results show that: the larger the pitch angle, the greater the peak vertical velocity of the aircraft, the greater the vertical displacement and the smaller the change in pitch deflection angle during the ditching process; the horizontal velocity of the airplane decreases faster and the horizontal displacement of the aircraft is smaller as the pitch angle decreases; when the aircraft ditches with a 6° pitch angle, it is subjected to the largest horizontal force, and therefore stops in the shortest time; when the aircraft ditches with a 14° pitch angle, the vertical force is the largest, and meanwhile the submerged displacement is the largest.

Key words: twin-fuselage aircraft, water forced landing, URANS method, VOF method, pitch angle

SUN Xiaoyuan, DENG Feng, LIU Xueqiang. Numerical Simulation of Ditching of a Twin-Fuselage Aircraft[J]. Acta Armamentarii, 2023, 44(7): 2066-2079.

Figures/Tables 23

Fig.1 Flowchart of numerical simulation

Fig.2 Schematic diagram of the phase intersection interface

Fig.3 6DOF in space of objects

Fig.4 Three views of the aircraft

Fig.5 Boundary conditions

Fig.6 Global grid area and mobile grid area

Fig.7 Pressure contour and phase contour after pretreatment

Table 1 Details of four different grids

网格序号	整体网格区域网格单元尺寸/m	移动网格区域网格单元尺寸/m	整体网格区域网格单元数/ 万个	移动网格区域网格单元数/ 万个	网格单元总数/ 万个
网格1	0.45	0.03	443	207	650
网格2	0.4	0.03	616	207	823
网格3	0.4	0.025	616	426	1042
网格4	0.4	0.02	616	601	1217

Fig.8 Comparison of simulation results of different grids

Fig.9 Geometrical properties of the plate

Fig.10 Comparison between experimentally obtained and numerically calculated skipping attitudes of the plate over water surface (Ω=65rot/s, the top is the experimental result, and the bottom is the simulation result)

Fig.11 Comparison between experimentally obtained and numerically calculated skipping attitudes of the plate over water surface (Ω=0rot/s, the top is the experimental result, and the bottom is the numerical simulation result)

Fig.12 When β=20°, the minimum throwing speed of the plate with different values of α

Fig.13 Pitch angle

Table 2 Mass attributes of the aircraft at different pitch angles

俯仰角度	质心坐标/m	质量/kg	I_xx/(kg·m²)	I_yy/(kg·m²)	I_zz/(kg·m²)	I_xy/(kg·m²)
6°	(0,0,0)	365.122	556.250	1128.107	656.731	-65.879
8°	(0,0,0)	365.122	552.351	1132.006	656.731	-45.773
10°	(0,0,0)	365.122	549.864	1134.495	656.731	-25.445
12°	(0,0,0)	365.122	548.801	1135.558	656.731	-4.992
14°	(0,0,0)	365.122	549.167	1135.192	656.731	15.486

Fig.14 Aircraft attitude and water surface changes at different times (the top is the aircraft attitude contour, and the bottom is the water surface change contour)

Fig.15 Phase countours at different moments (the top is the aircraft side phase contour, and the bottom is the aircraft bottom water immersion phase contour)

Fig.16 Pitch deflection angle varying with time

Fig.17 Pressure contours at different moments

Fig.18 Vertical velocity and vertical displacement varying with time

Fig.19 Horizontal velocity and horizontal displacement varying with time

Fig.20 Vertical force and vertical acceleration varying with time

Fig.21 Horizontal force and horizontal acceleration varying with time

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