Study Of Dynamic Grid Deformationical Algorithm And Its Application

Numerical simulation of unsteady flow problems involving moving boundaries has already become a hot spot of the Computational Fluid Dynamics (CFD) in the world, and the generation of dynamic grid is an essential technology within it.At present, spring analogy and elasticity body analogy have been used widely. The elasticity approach has stronger capability of the mesh deformation than the spring analogy method, but the efficiency is lower. For that reason, spring analogy method is used more frequently than elasticity approach. In fact, many unsteady flow problems involving moving boundaries have a large deformation.The quality of the dynamic grids generated by spring analogy method are difficult to satisfy the demands. Although the local remeshing method can deal with the problem of large mesh deformation, the error of interpolation can be introduced and the computation efficiency is low.In this dissertation, a new dynamic grid generation technique based on Delaunay graph has been studied and improved. In this method, a Delaunay graph of the solution domain is first generated, which can be moved easily during the geometric dynamic deformation. A one to one mapping between the Delaunay graph and the computational grid is maintained during the movement. Therefore the new computational grid after the dynamic movement can be generated efficiently through the mapping while maintaining the primary qualities of the grid. This method is non-iterative and much more efficient, and moreover, it offers both geometric and cell topology flexibility, which is crucial for many unsteady flow problems involving moving boundaries and relative motions.And through comparing with spring analogy method, the dynamic grids method based on Delaunay graph has stronger ability of deformation, and higher efficiency, for the reason that no iteration is needed. The ability of deformation of dynamic grid has been enhacend by some techniques proposed in this dissertation.Finally, the accuracy and efficiency of this method is demonstrated through some typical unsteady flow test cases, including NACA0012 pitching airfoil, fish swimming, rudder surface deflection and so on.The results indicate that the mesh quality requirement is satisfied and the method can be used to numerical simulation of unsteady flow involving moving boundaries.