基于流固耦合方法的超声速降落伞呼吸行为及复杂流动机理的数值研究

In the Mars exploration mission, a supersonic parachute plays a crucial role in the entry, descent and landing of the Mars rover. However, when the parachute deploys and works at supersonic speeds in the lower Martian atmosphere, a supersonic canopy breathing phenomenon is observed, shock waves form around the suspension lines, and the canopy fabric and suspension lines are mutually interactive with the complicated unsteady flow fields around a supersonic parachute, which causes the parachute drag decrease and the flow instability increase. However, in the Martian atmosphere, the complicated flows including suspension-line shock waves around a supersonic parachute and the fluid-structure interaction mechanism in canopy breathing phenomenon still remain unknown. In the proposal, the structural dynamics models of the canopy and suspension lines will be built to solve the fluid-structure interaction problem involving supersonic parachute. Based on the models proposed, numerical simulations of supersonic flows over rigid/flexible parachute models (both including the flexible suspension lines) will be conducted to study the fluid-structure interaction between the suspension lines and the surrounding complicated flows, investigate the effect of the parameter change of suspension lines on the unsteady flow fields around the supersonic parachute models, analyze the mutual influence between the canopy breathing motion and the complicated flows including suspension-line shock waves in the Martian atmosphere, and propose a control method for the canopy breathing motion with the effect of Fluid-Structure Interaction. The outcome of the proposal will provide the theory foundation and technical ability for the 2020 Mars mission of our country.

超声速降落伞是火星探测任务中的有效减速手段，然而当降落伞在稀薄的火星大气和超声速条件下开伞和工作时，伞衣会出现呼吸变形，伞绳附近亦会形成伞绳激波，并且柔性伞衣伞绳结构又与其周围非定常流场之间相互耦合而彼此影响，这势必对超声速降落伞的阻力特性和稳定性能造成严重影响。可是火星大气环境中超声速降落伞周围包含伞绳激波的复杂流动特性及伞衣呼吸行为的流固耦合机理至今尚未明了。本项目拟构建流固耦合作用下的伞衣伞绳的结构模型，开展刚性和柔性降落伞模型(均包含柔性伞绳)的数值模拟研究，分析柔性伞绳与周围流场的流固耦合过程，探讨伞绳结构参数变化对非定常流场结构的影响规律，解析火星大气条件下超声速降落伞呼吸行为与包含伞绳激波的复杂流场之间的相互影响机理，并提出流固耦合作用下伞衣呼吸行为的控制方法。本项目的开展与推进可为我国2020年火星探测任务中降落伞的研制提供理论支持和技术储备。

当降落伞在稀薄的火星大气和超声速条件下开伞和工作时，伞衣会出现呼吸变形，伞绳附近亦会形成伞绳激波，并且柔性伞衣伞绳结构又与其周围非定常流场之间相互耦合而彼此影响。本项目构建了该流固耦合作用下的伞衣伞绳的结构模型，发展了适用超声速降落伞的考虑可压缩湍流的数值模拟技术，研制了适用于超声速降落伞伞绳一体化结构模型的浸入边界技术和流固耦合方法，并编制了相应的计算程序。基于研制的模型和数值方法，本项目开展了刚性和柔性降落伞模型的数值模拟研究，分析了刚柔性伞绳与周围流场的流固耦合过程及其影响差异，理解了伞绳对超声速降落伞复杂流动及其气动性能的影响机理,明确了超声速降落伞周围的复杂流动机理，着重解析了火星大气条件下超声速降落伞呼吸行为与复杂流场之间的相互影响机理，设计了一种适用于火星大环境中新型伞衣材料以提高其在低密度、低动压条件下的气动性能。另外，进一步的研究发现不同超声速降落伞结构设计及伞体孔隙率分配对超声速降落伞周围的复杂流动机理和气动特性影响显著。本项目的开展与推进为我国火星探测任务中降落伞的设计和研制提供了理论支持和技术储备。