Structured Overset Grid Approach And Its Applications

The unsteady flow with moving boundary is often encountered in aerospace engineering, such asstore separation. In this problem, the aerodynamic force is highly unsteady and it can make thetrajectory of moving object change greatly. Computational Fluid Dynamics (CFD) can be used topredict such problem. In CFD method, dynamic overset grids method is applied widely in such flowdue to the high efficiency of dynamic grid. The traditional overset structured grids method has somedisadvantages, like low grid assembly efficiency and the degree of automation. It often needs manualintervention, while the numerical solution based on the overset structured grids method is highlyefficient. Overset unstructured grids method has a high efficiency of grid assembly and a high degreeof automation, but the numerical solution is not efficient enough. In the simulation of unsteady flowwith moving boundary, the efficiency of grids assembly and numerical solution is very important dueto the large number of physical time steps. Therefore, the overset structured grids method isinvestigated by using the concept of overset unstructured grids method. In this thesis, an oversetstructured grids algorithm with high efficiency and automation is proposed and the correspondingnumerical simulation program is developed. There are four parts in this thesis as followed：1) The numerical method based on structured grids is discussed. The Compressible Euler/N-Sequations are solved by the finite volume method in spatial discretization and the explicit multistagedual time-stepping scheme in temporal discritization. The Roe scheme is implemented to evaluate theconvective flux and the turbulent viscosity is evaluated by S-A or SST turbulence model.2) The overset structured grids assembly method is investigated. The concept of oversetunstructured grids is extended to overset structured grids method by combining the features of oversetstructured grids, Several issues are researched in overset grids assembly, such as donor cells searching,inter-grid boundary definition, interpolation boundary definition and its optimization.3) The overset structured grids method proposed is extended to the numerical simulation ofunsteady flow with moving boundary. Dynamic overset structured grids method is investigated andthe numerical algorithm with high efficiency and automation is proposed. The numerical simulationprograms are developed at the final.4) A number of cases are used to test the dynamic overset structured grids method developed inthis thesis The results show that this method is not only highly efficient but also automatic.