光滑粒子动力学（SPH）在轴向流动-固体耦合问题的应用研究

FSI (fluid-structure interaction) in axial flows is of interest for many engineering applications, such as the design of heat-exchanger tubes and high-speed trains, and vibrations of fuel rods in nuclear reactors. For this problem, the increase of the flow velocity or the decrease of the structure stiffness may induce the system instability, resulting in the large deformation or strong vibration of the structure. When ALE (Arbitrary Lagrangian-Eulerian) scheme based on mesh method is applied for solving this problem, the mesh needs to be updated in the simulation and the quality of the mesh may become bad due to the large deformation of the computational domain, reducing the simulation accuracy. In addition, it may be not easy to implement the monolithic scheme for the flow and structure solvers’ couple in this situation. SPH (Smoothed particle hydrodynamics), a meshfree method based on Lagrange description, was developed in recent years. In SPH simulation, there is no need to update mesh and it becomes easier to implement the monolithic scheme for the flow and structure solvers’ couple. Therefore, in this project, to overcome the limitation of the ALE method, SPH will be applied to numerically simulate the FSI in axial flows. The schemes of boundary conditions processing and fluid-structure solvers’ couple based on SPH are studied firstly and then the nonlinear dynamic characteristics, the flow field and the vibration of the structure are numerically studied with SPH. The study of this project will help improve SPH and provide references for other similar simulations.

轴向流动-固体耦合问题大量存在于工程应用中，如热交换器的管道设计、高速火车的设计以及核反应堆中燃料棒的振动等。在这类问题中，流速增大或固体刚度变小会导致系统发生不稳定现象，使结构产生大变形或者振动增强。采用基于网格法的ALE（Arbitrary Lagrangian-Eulerian）方法对这类问题进行数值模拟时，需要更新网格，大变形可能引起网格畸变，降低计算精度。此外，采用ALE方法时，流体和固体求解器全耦合较为困难。光滑粒子动力学（SPH）是近年来发展的一种基于拉格朗日描述的无网格法，计算中无需网格，能较容易地实现流体和固体求解器全耦合。为了突破ALE方法的限制，本项目拟采用SPH对轴向流动-固体耦合问题进行数值模拟，开展基于SPH的边界处理方法和流固耦合方法研究，数值研究系统的非线性动力学特性以及相应的流场、结构振动特征等。本项目的开展有助于完善SPH方法，为其他计算问题提供参考。

轴向流动-固体耦合问题大量存在于工程应用中，如热交换器的管道设计、高速火车的设计以及核反应堆中燃料棒的振动等。在这类问题中，流速增大或固体刚度变小会导致系统发生不稳定现象，使结构产生大变形或者振动增强。采用基于网格法的ALE（Arbitrary Lagrangian-Eulerian）方法对这类问题进行数值模拟时，需要更新网格，大变形可能引起网格畸变，降低计算精度。此外，采用ALE方法时，流体和固体求解器全耦合较为困难。光滑粒子动力学（SPH）是近年来发展的一种基于拉格朗日描述的无网格法，计算中无需网格，能较容易地实现流体和固体求解器全耦合。为了突破ALE方法的限制，本项目针对轴向流动-固体耦合问题，开展SPH（Smoothed Particle Hydrodynamics，光滑粒子动力学）数值方法（离散方法、边界条件处理以及并行计算等）研究，本项目主要进行了如下研究：.（1）针对不同雷诺数的Poiseuille流动开展SPH模拟，发现与粒子分布相关的不稳定在较高雷诺数时不存在，并提出一种较为简单的方法解决低雷诺数时与粒子分布相关的不稳定。.（2）结合有限差分法和SPH离散方法提出一种管道流动中进出口边界条件处理方法，该方法能够避免在SPH数值计算中使用周期边界条件处理管道流动。.（3）基于并行计算中网格分发的方法和SPH离散方法，建立一种可以用于一般问题SPH并行数值计算的粒子分发方法。.此外，项目还对流固耦合的SPH方法进行了研究，以满足轴向流动-固体耦合问题SPH数值计算的需要。