Cell-center ADT algorithm based on ghost cell

For the point search problem in Chimera gird generation, an alternating digital tree(ADT) method based on ghost cells was presented, which operated directly on the cell-centered grid system. The problem caused by the covering area incompleteness of cell-centered grids when constituting ADT data structure can be avoided by introducing ghost cells through extension of the original grid. The result of ADT searching with this method is a list of cell-centered cells, which can be directly traversed to obtain the exact donor cell. Therefore, the Stencil Walk method can be omitted. The use of ghost cells makes point search procedures near the boundary more flexible, providing exact information of donor cell near boundaries, and simplifying the construction of ghost cell system. One major application of the proposed method is expanding the types of the overset boundaries, as the constructed searching space is able to cover the entire grid, resolving the problem for the symmetry plane overset. The test case shows that the method is very reliable, feasible for boundaries, and greatly improves the flexibility of the Chimera grid for complex configurations.