超声速流中刚体系统分离与绳系控制的数值模拟

发布时间：2018-04-13 22:25

本文选题：动边界 + 多体分离　；参考：《大连理工大学》2016年博士论文

【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。
[Abstract]:A large number of problems in fluid mechanics involve moving boundaries, so the study of these problems is of great theoretical and practical value.The separation motion of rigid body system in supersonic flow not only has moving boundary, but also involves the interaction of shock wave and turbulence, which is a challenging subject.In this paper, the dynamic separation process of free rigid body system and rope rigid body system in supersonic flow is studied with the background of orbit prediction and landing point control in the process of falling and reentry of large and complex spacecraft. After reasonable simplification, the dynamic separation process of the free rigid body system and the rope rigid body system in supersonic flow is studied.In software, a six-degree-of-freedom rigid body solver is developed. The rigid body attitude is described by quaternion, and the rotation motion is numerically solved by the fourth-order Runge-Kutta method.By manipulating triangular mesh on the surface of rigid body in real time, it can deal with rigid body with complex shape and has the ability to make rigid body deform actively.Then it is coupled with the fluid solver in open source software package VTF. The fluid solver transfers boundary pressure information to the rigid body solver, and the rigid body solver transfers the surface grid node position and velocity information to the fluid solver.Level-set and ghost-fluid method are used to apply the inner boundary condition.Finally, a parallel adaptive fluid-solid coupling solver can be used to simulate 3D moving boundary problems.The reliability of the program is verified by a series of numerical experiments.In the case of free rigid body system, the separation motion of the system with different configurations in four Mach supersonic flow is simulated.The relationship between lateral velocity and flow velocity of rigid body and mass ratio of rigid body, initial distance and rotation motion are studied.Through qualitative and quantitative analysis, the process of separating motion of free rigid body system is further understood.The results show that the lateral separation velocity of rigid body reaches the maximum when it moves along the shock wave in the form of "surfing".Given the mass ratio, there is a specific initial distance or a given initial distance, so that the rigid body moves along the shock wave.The shape of the rigid body will affect the rotation of the object, and the rotation will further increase the lateral velocity generated by the "surfing" movement.The study also found that, when the reentry craft returns to Earth, more symmetrical internal components will make it spread out in a smaller rope-based rigid body system.The separation motion of rope system with different configurations in four Mach supersonic flow is simulated.The relationship between the velocity of flow direction of the system centroid and the large rigid body, the dispersion degree of the system and the mass ratio of the rigid body and the length of the rope system is studied emphatically.Through qualitative and quantitative analysis, it is found that the existence of rope can reduce the dispersion range of rigid system effectively, and change the velocity of flow direction of system centroid.The increase or decrease of the flow velocity of the mass center of the system is related to the mass ratio of the rigid body.For rigid body systems with the same components, the presence of rope makes the system less resistant.In contrast, for a falling rigid body made up of different components, the appearance of the rope increases the resistance of the system.
【学位授予单位】：大连理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O35

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