攻角效应对降落伞拉直过程影响的仿真模拟

Simulation of the effect of attack angle on ejection and deployment of a parachute

降落伞的弹射拉直过程是降落伞工作的第一个关键动作,能为后续降落伞顺利充气创造条件。降落伞的弹射拉直过程一般处于飞行器尾流区域,尾流特性对该过程具有重要影响。开伞时飞行器的高度、 Mach数、攻角等均会对飞行器尾流造成影响,其中开伞时飞行器攻角是降落伞设计中的一个重要考虑因素。该文采用三维非定常Reynolds平均N-S(unsteady Reynolds averaged Navier-Stokes,URANS)方程耦合六自由度(six degrees of freedom,6DoF)运动方程的方法,针对攻角效应对降落伞弹射拉直过程影响进行了研究。结果表明:攻角效应会显著改变飞行器尾流特性,与0°攻角相比,非0°攻角返回舱尾流呈现非对称流动特征,进而导致尾流方向与弹射初始速度方向不一致;非对称尾流会对分离体轨迹和姿态产生较大影响;攻角效应会导致分离体与尾流相对位置改变,从而影响拉直过程时间,即随着开伞攻角增加,弹射拉直时间减少。该方法和结论对于降落伞系统设计具有重要的参考价值。

[Objective] Ejection and deployment are the first key actions in the working process of a parachute, thereby resulting in its inflation. Ejection and deployment typically work in the wake of space crafts;therefore, the wake greatly influences the process. The conditions of the free stream may affect the wake flow, such as the attitude, Mach number, and angle of attack. Consequently, the angle of attack of an aircraft is an important consideration in parachute design. [Methods] Ejection and deployment are related to multiple factors, including fluid dynamics, multibody separation, and flexibility deformation. Owing to the advantages of fluid field information and low cost, computation fluid dynamics has become a powerful tool for solving engineering problems regarding fluids. This article focuses on the effect of attack angle on the ejection and deployment of a parachute. Based on the overset grid technology, the three-dimensional unsteady Reynolds averaged Navier-Stokes(URANS) coupled with a six-degrees-of-freedom(6DoF) equation of motion is applied to the research. The simulation consists of two steps: the static flow field simulation and the dynamic separation process based on the static flow field. [Results] The simulation results showed the following:(1) The negative aero force at 0° angle of attack in the recirculation zone hindered the separator department.(2) The wake during the 0° angle of attack was parallel to the axis of capsule;however, 10° and 20° angles of attack demonstrated an obvious deviation from the axis.(3) The separator showed almost no attitude variation for 0° angle of attack, whereas an obvious attitude variation for 10° and 20° angles of attack resulted from the direction of the wake.(4) An obvious interaction occurred between the wake behind the capsule and shock before the separator. [Conclusions] The following conclusions can be drawn from the research: The effects of the angle of attack significantly change the characteristics of the wake. Compared with the 0° condition, the capsule wakes present an asymmetric character in the other two conditions. What’s more, the wake shows an obvious deviation from the direction of the initial separated velocity;the asymmetrical wake will affect the trajectory and attitude of the separator;and the effect of the angle of attack will change the relative position between the capsule and the separator and influence the separated time: the time of ejection and deployment will be reduced with an increase in the angle of attack. The method and the conclusions can provide a valuable reference for the validation and design of the recovery system.