Parallel computing of overset grids for aerodynamic problems with moving objects

Aerodynamic problems involving moving objects have many applications, including store separation, fluid-structure interaction, takeoff and landing, and fast maneuverability. While wind tunnel or flight test remain important, time accurate computational fluid dynamics (CFD) offers the option of calculating these procedures from first principles. However, such computations are complicated and time consuming. Parallel computing offers a very effective way to improve our productivity in doing CFD analysis. In this article, we review recent progress made in parallel computing in this area. The store separation problem will be used to offer a physical focus and to help motivate the research effort. The chimera grid technique will be emphasized due to its flexibility and wide use in the technical community. In the Chimera grid scheme, a set of independent, overlapping, structured grids are used to decompose the domain of interest. This allows the use of efficient structured grid flow solvers and associated boundary conditions, and allows for grid motion without stretching or regridding. However, these advantages are gained in exchange for the requirement to establish communication links between the overlapping grids via a process referred to as `grid assembly.' Logical, incremental steps are presented in the parallel implementation of the grid assembly function. Issues related to data structure, processor-to-processor communication, parallel efficiency, and assessment of run time improvement are addressed in detail. In a practical application, the current practice allows the CPU time to be reduced from 6.5 days on a single processor computer to about 4 h on a parallel computer.