Numerical Simulation Technique Research And Experiment Verification For Unsteady Multi-Body Flowfield Involving Relative Movement

Flow problem about Multi-body with relative movement is a special kind of mechanical problem and it widely exists in the field of aeronautics, astronautics and weapons. Because of its complexity, it is hard to research or analysis whether using experimental or numerical simulation methods. As a result, establishing an effective and accurate numerical simulation method is important both in theory and practice. In this dissertation, a numerical method using dynamic unstructured grid is studied and software system is established, which can efficiently and exactly simulate multi-body flow problems with complex configuration and complicated relative motion. The reliability of the simulation system is proved by numerical and experimental verification and it has achieved good effect in application.Firstly, considering the request of efficiency and precision in numerical simulation, the Arbitrary-Lagrangian Eulerian (ALE) framework is chosen to solve 3D time-dependent Euler equations and the Van Leer scheme is applied for spatial discretization. Piecewise linear reconstruction or MUSCL reconstruction is used to obtain second-order spatial accuracy and a multi-stage Runge-Kutta time stepping scheme is adopted for second-order temporal accuracy. To eliminate non-physical oscillations near discontinuities, the limiters of Barth & Jespersen and Venkarakrishnan are employed. Furthermore, the 6DOF (degree of freedom) trajectory equations of rigid body dynamics are coupled in the overall algorithm, in which aerodynamic forces and rigid body movements are updated at the same physics time step with loosing coupling.Secondly, considering the request for complex configuration and body motion, the dynamic unstructured grid method is studied. The mesh movement strategy is implemented by the combination of mesh deformation and local remeshing. The improved spring analogy model is used to control mesh deformation, which is sufficient for cases with small relative boundary displacement. For cases with relative large boundary displacement, when the mesh elements are severely deformed, Delaunay remeshing method is used to regenerate mesh. Thereon, an automatic technique is studied, which includes the procedure of checking mesh quality, extracting the reconstructed windows, regenerating meshes, finding relationship between new and old grids and transferring solutions from the old mesh to the new one. The new data transfer method, called "moving mesh transfer method", is innovatively proposed to avoid accumulation of interpolation errors. This highly accurate data transferring is implemented by mesh movement strategy, which succeeds in solving one dimensional, two dimensional and three dimensional problems. The "octree" data structure is also used to accelerate the searching operation during interpolation.Thirdly, considering the verification and validation of numerical method, numerical simulation of the flow field around the space shuttle and a civilian aircraft is performed and the results are consistent with the experiment data and CFD results in references. In addition, an experiment is specially designed on shock tube to validate the numerical method. The numerical simulation of Ping-Pong's trajectory agrees well with those obtained in experiment. This simple and effective experiment can present verification and validation of numerical method, and offer reference for further experiment research and moving body experiment.Lastly, some multi-body flow problems with complex configuration are studied, such as fairing separation, interior weapon cabin's opening and cluster munitions dispersing. Aimed at the difficulty in simulating the procedure of two bodies separating from tangency to large displacement, a new method called "virtual mesh ventilation method" is introduced, and this method factually reproduces aerodynamic fluctuations at the beginning of fairing separation and flow-induced pressure oscillations in 3D cavity after the weapon cabin's door is open. In the research of fairing separation, after comprehensive analysis of factors such as fairing shape, interfering factors and centroid position, a new separation rule called "centroid backward rule" is proposed according to numerical simulation results with dynamic unstructured grid method, and this rule can be regarded as common criteria to ensure safety in fairing separation. Besides, a cluster munitions dispersing procedure, including cluster munitions rotating, cover ejection and plenty of bullets dispersion, is simulated using dynamic unstructured grid method. Results show that the software is competent for solving extraordinarily complicated problems, and it also offers an effective way to design and validate the cluster munitions.