Patched coordinate systems

Abstract : Numerical grid generation has been an excellent tool for producing curvilinear body-fitted coordinate systems. Curvilinear coordinate systems or grids are commonly used in the solution of partial differential equations in domains surrounding arbitrary geometrical boundary shapes. Body-fitted grids are particularly advantageous in the treatment of surface boundary conditions, and usually yield a degree of simplicity in the logic required to solve the hosted partial differential equations. In practice, numerical grid generation usually involves transformation of the physical domain of interest into a geometrically simple domain, such as a rectangular block or assembly of blocks. The solution of grid generation equations in the simple domain products the coordinates of a corresponding grid in the physical domain, subject to a variety of grid control procedures aimed at producing favorable grid characteristics. This process is usually straightforward when the topology of the physical domain is simple enough to allow transformation to a single rectangular domain. But when dealing with geometrically and topologically complex domains such as surround an aircraft configuration, the total issue of grid generation becomes more complex. The domain in general cannot be mapped into a single block. The configuration surface geometry itself may be nonanalytic, and these features will be manifest in any grid surrounding such complex boundary shapes.