Advance in overset grid schemes - From Chimera to DRAGON grids

A new approach that uses nonstructured mesh to replace the arbitrarily overlapped structured regions of embedded grids is presented. The present methodology uses the Chimera overlapped structured grids that are independently generated and body fitted, yielding a high-quality grid readily accessible for efficient solution schemes. A hybrid grid scheme is then proposed that maximizes the advantages of the Chimera scheme and adapts the strengths of the unstructured grid while at the same time keeps its weaknesses minimal. This new adaptation to the Chimera thinking is the direct replacement of arbitrary grid overlapping by nonstructured (DRAGON) grid. The nonstructured grid region sandwiched between the structured grids is limited in size, resulting in only a small increase in memory and computational effort. The DRAGON grid method has three important advantages: 1) preserving strengths of the Chimera grid, 2) eliminating difficulties sometimes encountered in the Chimera scheme, and 3) making grid communication in a fully conservative and consistent manner insofar as the governing equations are concerned. Numerical results on representative two-dimensional steady and unsteady inviscid flows are demonstrated.