The inflation process and safety analyses of a parachute ejected from civil aircrafts
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摘要:
当降落伞牵引小质量负荷（应急数据记录系统）从大型民用飞机机身下方弹射离机时，不同于弹体等刚性物体，柔性伞衣充气过程中剐蹭机身等安全隐患更大。为了研究弹射降落伞离机充气过程气动特性和运动轨迹，采用任意拉格朗日-欧拉（arbitrary Lagrange Euler, ALE）方法，对不同来流速度和角度条件下的降落伞开伞过程、气动特性和流场特性进行了数值模拟，分析了来流速度和角度对伞衣充气过程的影响。结果表明：当伞衣贴近或挤压机身时，伞衣侧面剪切层和近尾迹区中的涡运动都会受到机身影响，但降落伞不会完全失效，这时伞衣投影面积相对较小，充气过程的动载峰值变小。同时，在 40～160 m/s来流速度、临界来流迎角下，给出了降落伞可安全弹射离机的来流条件，为分离式飞机应急记录跟踪系统设计提供了理论支持。
Abstract:The ejectable emergency flight data recorder equipped with a parachute show promising prospects in aircraft safety and rescue. However, compared to rigid objects, the flexible canopy of an ejected parachute during its inflation process is more likely to collide with the fuselage, which brings potential safety hazards. Therefore, the aerodynamic characteristics and trajectories of a parachute ejected from a civil aircraft are studied numerically by the Arbitrary Lagrange Euler method (ALE). The effects of the free-stream conditions, i.e., the velocity and angle of attack on the parachute inflation process, aerodynamic characteristics, and flow fields are analyzed. Results show that when the parachute is close to the fuselage, the shear layers and vortical motions around the canopy are modified by the fuselage. Nevertheless, the parachute does not fail completely. Meanwhile, the projected area and opening load of the canopy are relatively small. The critical angle of attack of at the free-stream with velocity bewteen 40 m/s and 160 m/s is obtained. The safety condition for ejections is given at last. This work provides a theoretical support for the design of ejectable flight data recording and emergency tracking systems.
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Key words:
- aircraft safety and rescue /
- parachute /
- finite mass inflation /
- numerical simulation /
- safety analyses
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图 2 试验和数值模拟中的开伞动载
Figure 2. The parachute opening loads in experiments and numerical simulation
图 5 降落伞与机身尾部相对位置示意图
Figure 5. Schematic diagram of the relative position between a parachute and a fuselage tail
图 6 动载峰值时刻伞衣与机身的距离
Figure 6. The distance between a parachute and a fuselage when the opening load reaches its maximum
图 7 动载峰值时刻伞衣对称面的压力云图，等值线为流向速度
Figure 7. Flow fields at the parachute symmetrical plane (Shade and line contours denote pressure and streamwise velocity, respectively)
图 8 动载峰值时刻伞衣对称面的Lamb矢量散度云图
Figure 8. Divergence of the Lamb vector at the parachute symmetrical plane
图 9 伞衣对称面的涡量和涡量动力学方程中前三项的幅值(
${U_\infty } = 160\;{\rm{m/s}},{\rm{ }}\alpha =30^\circ$ )
Figure 9. The magnitude of vorticity and the first three terms in the vorticity dynamics equation at the parachute symmetrical plane (
${U_\infty } = 160\;{\rm{m/s}},{\rm{ }}\alpha =30^\circ$) 
图 11 伞衣对称面的涡量和涡量动力学方程中前三项的幅值(
${U_\infty } = 100\;{\rm{m/s}},{\rm{ }}\alpha =0^\circ$ )
Figure 11. The magnitude of vorticity and the first three terms in the vorticity dynamics equation at the parachute symmetrical plane (
${U_\infty } = 100\;{\rm{m/s}},{\rm{ }}\alpha =0^\circ$ )
图 10 伞衣对称面的涡量和涡量动力学方程中前三项的幅值(
${U_\infty } = 100\;{\rm{m/s}},{\rm{ }}\alpha =30^\circ$ )
Figure 10. The magnitude of vorticity and the first three terms in the vorticity dynamics equation at the parachute symmetrical plane (
${U_\infty } = 100\;{\rm{m/s}},{\rm{ }}\alpha =30^\circ$ )
图 12 伞衣充气过程中的动载与投影面积(
${U_\infty } = 100\;{\rm{m/s}}$ )
Figure 12. The opening load and projected area during the parachute inflation process (
${U_\infty } = 100\;{\rm{m/s}}$ )
图 13 伞衣在充气过程中的外形变化(
${U_\infty } = 100\;{\rm{m/s}},{\rm{ }}\alpha {\rm{ = }}30^\circ$ )
Figure 13. The canopy deformation during the parachute inflation process (
${U_\infty } = 100\;{\rm{m/s}},{\rm{ }}\alpha {\rm{ = }}30^\circ$ )
图 14 不同来流速度和弹射速度下，伞衣在充气过程中的外形变化
Figure 14. The canopy deformation during the parachute inflation process at different free-stream velocities and eject velocities
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