笛卡儿坐标系
Most of the fluid flow equations are easily solved by discretizing procedures using the Cartesian coordinate system. In this system the implementation of finite volume method is simpler and easier to understand. But most of the engineering problems deal with complex geometries that don’t work well in the Cartesian coordinate system. When the boundary region of the flow does not coincide with the coordinate lines of the structured grid then we can solve the problem by geometry approximation. Figures 1a. and 1b. shows how a cylinder can be approximated with the Cartesian coordinate system.