降落伞稳降阶段的SPH方法数值模拟

摘要

With the rise of computer technology and numerical simulation, it is possible to describe accu-rately the dynamic chatacteristics of parachute. In order to eliminate the influence of negative volume due to large mesh deformation in the traditional parachute simulation, this article uses Smoothed Particle Hydrodynam-ics (SPH) method. The steady-state descent phase of parachute is numerically simulated, and the aerodynamic coefficients are consistent with wind tunnel test results. The influence of air particle density on the numerical results is investigated. It turns out that an effective coupling of the parachute structure with the flow field is dif-ficult to be achieved in low particle density condition, which reduces the calculation accuracy. However, when the particle density exceeds a certain value, the computational consumption will increase and the calculation ac-curacy will be affected because of the rounding error. Therefore, the optimal particle number is determined. On this basis, the descent processes of parachute with different initial velocities are simulated. The dynamic change of the canopy shape, the projected diameter, the drop speed, the aerodynamic force and the swinging angle are obtained. It is found that the velocity has less impact on the parachute breath rate, the balancing speed as well as the aerodynamic force. The canopy breath amplitude and the swinging angle increase as the velocity increase, and the attenuation property of swinging angle is lower than the project diameter. SPH method can effectively avoid large grid deformation problems in the aspect of parachute fluid-structure interaction and has wide appli-cation prospects in the field of large deformation on flexible fabric with fluid-structure interaction method.%随着计算机技术的不断发展以及数值模拟技术的兴起，对降落伞力学特性的模拟日益精确。为了消除传统降落伞模拟中因网格大变形而产生负体积的影响，文章采用光滑粒子流体动力学方法，对选定降落伞模型开展了稳降阶段的流固耦合数值模拟，计算得到的气动力系数与风洞试验结果较为一致。研究了空气粒子密度对数值结果的影响，结果表明，粒子密度过少，降落伞结构单元难以和流场实现有效耦合，计算精度降低；但粒子密度超过一定值，不仅会增加计算消耗，也会增加舍入误差而影响计算精度，确定了最佳粒子数。在此基础上，模拟了不同初速度下降落伞的下降过程，获得了降落伞外形、投影直径、下降速度、降落伞气动力及伞衣摆角的动态变化情况。数值结果表明伞衣的呼吸频率、稳定后的平衡速度和气动力受速度影响较小，但速度增加，伞衣呼吸强度及摆角增加，且摆动角度的衰减性要低于投影直径的衰减能力。SPH模拟方法有效地回避了降落伞流固耦合的网格大变形问题，在柔性大变形流固耦合问题上有广阔的应用前景。