A Hybrid Overset Grid Approach Based On Adaptive Cartesian Grid

Multiple bodies separation is often encountered in aerospace engineering. The complex unsteady flow field between bodies can cause a strong aerodynamic interference, which is often detrimental and even can threaten the safety of flight. In the past, flight test and wind tunnel test are the main means to deal with this problem, with the abuse of high risk, high cost and long cycle. In recent years, computational fluid dynamics is widely used in these problems. Dynamic overset grid technique is very suitable to deal with the unsteady flow fields past multiple bodies in relatively moving, without mesh regeneration. It can guarantee the mesh quality. Both overset structured grids and overset unstructured grids can accurately calculate the aerodynamic, but they need to adjust the grid scale of the boundary to avoid the numerical dissipation caused by ‘dig-hole'. Restricted by the data structure of structured grid and unstructured grid, it has to increase the number of grid to ensure the consistency of grid scale, which puts forward higher demands on computer resources and reduces the efficiency of numerical calculation. In this thesis, a hybrid overset grids method based on adaptive Cartesian grid is proposed and a N-S solver is developed.First of all, the numerical methods are introduced. The steady/unsteady Euler/N-S equations are solved by the finite volume method in spatial discretization and the explicit multistage dual time-stepping scheme in temporal discritization. The JST scheme is implemented to evaluate the convective flux and the turbulent viscosity is evaluated by S-A model. Then, the assembly method of hybrid overset grids based on adaptive Cartesian grid is investigated. The inter-grid boundary definition method of overset unstructured grids is used. To improve the computational efficiency, a neighbour-to-neighbour searching algorithm is used. At last, a dynamic hybrid overset grids method based on adaptive Cartesian grid is developed, which is verified by the standard example. A number of cases are used to test the N-S solver based on the hybrid overset grids method proposed in the thesis. The results show that the hybrid overset grids method and the solver are highly efficient.