【作者】 李涛；

【导师】 吴锤结；

【作者基本信息】 大连理工大学 ， 力学—流体力学， 2016， 博士

【摘要】 流体力学中大量问题涉及到动边界,对这类问题的研究有很重要的理论和应用价值。超声速流中刚体系统的分离运动不仅存在动边界,还涉及到激波、湍流等多物理过程相互作用,是一个具有挑战性的课题。本文以大型复杂航天器陨落再入过程中的轨道预测和落点控制为研究背景,经过合理简化,研究了超声速流中自由刚体系统和绳系刚体系统的动态分离过程。软件方面,首先开发了一个六自由度刚体求解器,刚体姿态使用四元数描述,旋转运动使用四阶Runge-Kutta法数值求解。通过实时操作刚体表面三角形网格,它能够处理复杂形状的刚体,且具备使刚体发生主动变形的能力。然后使用松耦合算法,将它与开源软件包VTF中的流体求解器耦合,流体求解器传递边界压力信息给刚体求解器,刚体求解器传递表面网格节点位置和速度信息给流体求解器,采用level-set配合ghost-fluid方法施加内置边界条件。最终,得到了一个可用于模拟三维动边界问题的并行自适应流固耦合求解器。通过一系列数值实验,验证了程序的可靠性。自由刚体系统方面,模拟了不同构型的系统在四马赫的超声速流中的分离运动。着重研究了刚体的侧向速度和流向速度与刚体的质量比、初始间距和旋转运动的关系。通过定性和定量分析,加深了对自由刚体系统分离运动过程的理解。研究结果发现,刚体的侧向分离速度在其沿激波以类似“冲浪”的形式运动时达到最大。给定质量比,则存在特定的初始间距,或给定初始间距,则存在特定质量比使刚体沿激波运动。刚体的形状会影响物体的旋转运动,旋转运动又会进一步增大“冲浪”运动产生的侧向速度。研究结果还发现,在再入陨落飞行器返回地球时,对称性更好的内部组件的会使其散布范围更小绳系刚体系统方面,模拟了不同构型的绳系系统在四马赫的超声速流中的分离运动。着重研究了系统质心和较大刚体的流向速度以及系统的散布度与刚体的质量比、绳系长度的关系。通过定性和定量分析,发现绳子的存在首先能有效减小刚体系的散布范围,其次也会改变系统质心的流向速度。系统质心的流向速度增大或减小与刚体质量比有关。对于由相同部件构成的刚体系统,绳子的出现会使系统受到更小的阻力。与此相反,对于由不同部件构成的陨落刚体,绳子的出现会增大系统的阻力。更多还原

【Abstract】 Moving boundaries exist in a lot of fluid dynamics problems. The study of such problems has very important theoretical and practical value. The dynamic separation behavior of rigid body system in supersonic flow not only involves moving boundaries but also involves shock waves, turbulence, etc.. which makes it is a challenging problem. In this paper, the dynamic separation behavior of free rigid body system and tethered rigid body system in supersonic flow is conducted under the background of orbit prediction and control for large and complex spacecraft during their reentry process.To solve this, a 6-DOF solver is developed first which using quaternion to describe rigid body’orientation and using fourth order Runge-Kutta method to solve the rotational governing equations. This solver can deal with complex geometry by manipulates rigid bodie’s surfaces grid. Then, the 6-DOF solver is coupled with VTF’s fluid solver[10] using loose-coupling al-gorithm. The fluid solver send boundaries pressure to 6-DOF solver and The 6-DOF solver send boundaries position and velocity to fluid solver. Using level-set method and ghost-fluid method, immersed boundary conditions are enforced. Finally, a parallel software package for fluid structure interaction problems involving complex three dimension rigid body undergoing large displacements is established. The reliability of the solver is verified with a series of nu-merical experiments.The dynamic separate behavior of free rigid body system with different configurations in a supersonic flow (M=4) is simulated. The influence of mass ratio, initial spacing and rotary on the transverse velocity of rigid body is investigated. It is found that the body’s transverse velocity is maximum when the body fly along the shock front. At a critical mass ratio for a given initial spacing or at a critical initial spacing for a given critical mass ratio, the body fly along the shock front. The rotary can increase the transverse velocity. During the reentry process, to minimal the bodies’spread range, it is better to chose symmetrical components.The dynamic separate behavior of tethered rigid body system with different configurations in a supersonic flow (M=4) is simulated. The influence of mass ratio and tether length on the stream-wise velocity of system and the bigger body is investigated. By qualitative and parame-terized analyses, it is found that the tether can minimize the spread range of bodies and change the stream-wise velocity of the system. The mass ratio determine the stream-sise velocity of the system. For the system with identical bodies, the tether can decrease the aerodynamic forces on the system. In contrast, for the system different bodies, the tether can increase the aerodynamic forces on the system.更多还原